Optical Fiber Communication

Scientech 2501A

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Scientech 2501A Optical Fiber Communication

Optical Fiber Communication

Scientech 2501A
Table of Contents
Safety Instructions 4
Introduction 5
Features 6
Technical Specifications 7
Theory 8
Optical Fiber Communication System 8
Advantages of Fiber Optic System 17
Experiments
Experiment 1 48
Study of 650 nm Fiber Optic Analog link.
Experiment 2 50
Study of 650 nm Fiber Optic Digital Link.
Experiment 3 52
To obtain Intensity Modulation of the Analog Signal & Demodulation
Experiment 4 55
To obtain Intensity Modulation of the Digital Signal & Demodulation
Experiment 5 58
Study of Frequency Modulation (FM)
Experiment 6 62
Study of Pulse Width Modulation
Experiment 7 66
Measurement of Propagation or Attenuation Loss in the optical fiber
Experiment 8 69
Study of Bending Loss
Experiment 9 71
Measurement of Optical Power using optical power meter
Experiment 10 73
Measurement of Propagation Loss in optical fiber using POM
Experiment 11 75
Measurement of Numerical Aperture (NA) of optical fiber
Experiment 12 78
Study of Characteristics of E-O converter using optical power meter

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Scientech 2501A Optical Fiber Communication

Experiment 13 80
Study of Characteristics of Fiber Optic Communication Link
Experiment 14 ` 82
Study of Voice Communication through fiber Optic cable using
Amplitude Modulation
Experiment 15 84
Demonstration of Voice Transmission through optical fiber using FM
Experiment 16 86
Study of Voice Transmission through optical fiber using PWM
Experiment 17 88
Study of the effects of Switched Fault Number 1 & 8 on Amplitude
Modulation System
Experiment 18 90
Study of the effects of Switched Fault Number 4, 5 & 7 in FM System
Experiment 19 92
Study of the effects of Switched Fault Number 2, 3 & 6 on Pulse Width
Modulation System
Experiment 20 94
Determination of Bit Rate supported by the fiber optic link
Experiment 21 96
Determination of Sensitivity of the fiber optic link
Experiment 22 98
Determination of Power Margin (Power Budget)
Experiment 23 100
V-I Characteristics of Photo LED
Experiment 24 102
V-I Characteristics of Photo Detector
Experiment 25 104
To Measure Bit Error Rate
Experiment 26 107
Study and Observation of Eye Pattern
● Experiment 27 112
Determination of effect of Electromagnetic Interference over a Copper
track and a Fiber Optic cable
Frequently Asked Questions 115
Glossary of Fiber Optic terms 123
Warranty & List of Contents 127

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Scientech 2501A Optical Fiber Communication
Safety Instructions
Read the following safety instructions carefully before operating the product.
To avoid any personal injury, or damage to the product, or any products connected to it;
Do not operate the instrument if you suspect any damage within.
The instrument should be serviced by qualified personnel only.
For your Safety:
Use proper Mains cord : Use only the mains cord designed for this product.
Ensure that the mains cord is suitable for your country.
Ground the Instrument : This product is grounded through the protective earth
conductor of the mains cord. To avoid electric shock the
grounding conductor must be connected to the earth
ground. Before making connections to the input
terminals, ensure that the instrument is properly
grounded.

Observe Terminal Ratings : To avoid fire or shock hazards, observe all ratings and
marks on the instrument.

Use only the proper Fuse : Use the fuse type and rating specified for this product.

Use in proper Atmosphere : Please refer to operating conditions given in the manual.
Do not operate in wet / damp conditions.
Do not operate in an explosive atmosphere.
Keep the product dust free, clean and dry.

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Scientech 2501A Optical Fiber Communication

Introduction

Fiber optic communication is a method of transmitting information from one place

another by sending pulses of light through an optical fiber. The light forms
electromagnetic carrier wave that is modulated to carry information. First developed in
the 1970s, fiber-optic communication systems have revolutionized the
telecommunications industry and have played a major role in the advent of the
Information Age. Because of its advantages over electrical transmission, optical fibers
have largely replaced copper wire communications in core networks in the developed
world.

Optical Fiber

The process of communicating using fiber-optics involves the following basic steps:
Creating the optical signal involving the use of a transmitter, relaying the signal along
the fiber, ensuring that the signal does not become too distorted or weak, receiving the
optical signal, and converting it into an electrical signal.
Communication may be broadly defined as the transfer of information from one point to
another. Before Fiber Optics came along, the primary means of real time data
communication was electrical in nature. It was accomplished by using copper wire or by
modulating information on to an electromagnetic wave that acts as a carrier for the
information signal. All these methods have one problem in common the communication
had to be over a straight-line path. While, in Fiber Optic Communication, the optical
wave propagates inside the fiber and acquires the shape of the fiber.
Fiber Optics provides an alternative means of sending information over significant
distances using light energy. Light as utilized for communication has major advantages
because it can be modulated at significant higher frequencies than electrical signals. That
is till 1870, when an Irish physicist John Tyndall carried out a simple experiment. He
filled a container with water and shone light into it. In the dark room he pulled the bung
from the opposite end of the container. The light shone out in the direction of the curved
path of the water. The light was guided and a new science was born called Fiber Optics.
This was achieved due to the refraction property of the light, which made it possible to
get the light reflected inside the optical fiber with certain approaching angles within
desired threshold and continuing the process within the cable till the optical wave
reached the other end and thus the light propagated inside the optical fiber.

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Scientech 2501A Optical Fiber Communication

Features
● Simplex Analog and Digital Transreceiver
● 660 nm channel with Transmitter & Receiver
● AM-FM-PWM modulation / demodulation
● On board Function Generator
● On board Clock & PRBS Data Generator
● On board Bit Error Counter
● Crystal Controlled Clock
● Functional Blocks indicated on-board mimic
● Input-output & test points provided on board
● On board voice link
● Numerical Aperture measurement jig and mandrel for bending loss included
● Switched faults on Transmitter & Receiver
● Online Product Tutorials

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Scientech 2501A Optical Fiber Communication

Technical Specifications
Transmitter : 1 no., Fiber Optic LED, Wavelength 660 nm
Receiver : 1 no., Fiber Optic Photo detector
Modulation Techniques : AM, FM, PWM
Drivers : 1 no. with Analog & Digital modes
Clock : Crystal controlled Clock 4.096 MHz
PLL Detector : 1 no.
AC Amplifier : 1 no.
Comparator : 1 no.
Filter : 1 no. 4th order Butterworth, 3.4 KHz cut-off
frequency
Analog Band Width : 350 KHz
Digital Band Width : 2.5 MHz
Function Generator : 1 KHz Sine wave (Amplitude adjustable)
1 KHz Square wave (TTL)
Clock Generator : 64 KHz/128 KHz/256 KHz (TTL)
Data Generator : PRBS (15 Bit)
Noise Generator : Variable level
Bit Error Counter : 4 digits, 7 segment display
Voice Link : F. O. voice link using microphone & speaker
Switched Faults : 8 nos.
Fiber Optic Cable : Standard SMA Connector type
Cable Type : Step indexed multimode PMMA plastic cable
Core Refractive Index : 1.492
Clad Refractive Index : 1.406
Numerical Aperture : Better than 0.5
Acceptance Angle : Better than 60 deg.
Fiber Diameter : 1000 microns
Outer Diameter : 2.2 mm
Fiber Length : 0.5 m & 1 m
Test Points : 34 nos.
Inter connections : 2 mm sockets
Dimensions (mm) : W 326 × D 252 × H 52
Weight : 1 Kg approximately
Operating conditions : 0-400 C, 80% RH
Power Supply : 110-220 V, ±10%, 50/60 Hz
Power Consumption : 3 VA approximately
Product Tutorials : Online (on www.ScientechLearning.com).

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Scientech 2501A Optical Fiber Communication

Theory
Introduction to Optical Fiber: An optical fiber is a thin, flexible, transparent fiber
that acts as a waveguide, or "light pipe", to transmit light between the two ends of the
fiber. The field of applied science and engineering concerned with the design and
application of optical fibers is known as fiber optics. Optical fibers are widely used in
fiber-optic communications, which permits transmission over longer distances and at
higher bandwidths (data rates) than other forms of communication. Fibers are used
instead of metal wires because signals travel along them with less loss and are also
immune to electromagnetic interference. Fibers are also used for illumination, and are
wrapped in bundles so they can be used to carry images, thus allowing viewing in
tight spaces. Specially designed fibers are used for a variety of other applications,
including sensors and fiber lasers.

Optical Fiber Communication System

Optical Fiber Communication System

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Scientech 2501A Optical Fiber Communication

Understanding how Fiber optics are made and function for uses in everyday life is an
intriguing work of art combined with science. Fiber optics has been fabricated from
materials that transmit light and are made from a bundle of very thin glass or plastic
Fibers enclosed in a tube. One end is at a source of light and the other end is a camera
lens, used to channel light and images around the bends and corners. Fiber optics has
a highly transparent core of glass, or plastic encircled by a covering called "cladding".
Light is stimulated through a source on one end of the Fiber optic and as the light
travels through the tube, the cladding is there to keep it all inside. A bundle of Fiber
optics may be bent or twisted without distorting the image, as the cladding is designed
to reflect these lighting images from inside the surface. This Fiber optic light source
can carry light over mass distances, ranging from a few inches to over 100 miles.
There are two kinds of Fiber optics. The single-mode Fiber optic is used for high
speed and long distance transmissions because they have extremely tiny cores and
they accept light only along the axis of the Fibers. Tiny lasers send light directly into
the Fiber optic where there are low-loss connectors used to join the Fibers within the
system without substantially degrading the light signal. Then there are multi-mode
which have much larger cores and accept light from a variety of angles and can use
more types of light sources. Multi-mode Fiber optics also uses less expensive
connectors, but they cannot be used over long distances as with the single-mode Fiber
optics.
Fiber optics has a large variety of uses. Most common and widely used in
communication systems, Fiber optic communication systems have a variety of
features that make it superior to the systems that use the traditional copper cables. The
uses of fiber optics with these systems use a larger information-carrying capacity
where they are not hassled with electrical interference and require fewer amplifiers
then the copper cable systems. Fiber optic communication systems are installed in
large networks of Fiber optic bundles all around the world and even under the oceans.
Many Fiber optic testers are available to provide you with the best Fiber optic
equipment.

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Scientech 2501A Optical Fiber Communication

Optical Sources Laser and LED

In Fiber optic communication systems, lasers are used to transmit messages in
numeric code by flashing on and off at high speeds. This code can constitute a voice
or an electronic file containing, text, numbers, or illustrations, all by using Fiber
optics. The light from many lasers are added together onto a single Fiber optic
enabling thousands of currents of data to pass through a single Fiber optic cable at one
time. This data will travel through the Fiber optics and into interpreting devices to
convert the messages back into the form of its original signals. Industries also use
Fiber optics to measure temperatures, pressure, acceleration and voltage, among an
assortment of other uses.

Here, the information source provides an amplified electrical signal to a transmitter

comprising an electrical stage, which drives an optical source to give conversion, may
be either a semiconductor, LASER (Light Amplification by Stimulated Emission of
Radiation) or LED. The transmission medium consists of optical source, which
provides an electrical to optical conversion, an optical Fiber cable used for
transmission of signal and the receiver, consists of an optical detector, which drives a
further electrical stage and hence provides demodulation of optical carrier. This
electrical signal is amplified and applied to the destination. e.g. Speaker.

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Scientech 2501A Optical Fiber Communication

Photo diodes (P-I-N or Avalanche) and in some instances photo transistors and photo
conductors are utilized for detection of optical signal and optical to electrical
conversion. The optical carrier may be modulated using an analog or digital
information signal. Analog modulation involves the variation of light emitted from
the optical source in continuous manner. In digital modulation however, discrete
changes in the light intensity are obtained (i.e. ‘On-Off’ pulses) although often
simpler to implement, analog modulation with an optical Fiber communication system
is less efficient, requiring a far higher signal to noise ratio (SNR) at the receiver than
digital modulation. Also, linearity needed for analog modulation is not provided by
semiconductor optical sources especially at high modulation frequencies.
Principle of operation of Optical Fiber:
The principle of operation of optical Fiber lies in the behaviour of light. It is a widely
held view that light always travels in straight line and at constant speed. Of course,
the light propagates in straight lines, but when it is reflected inside the optical Fiber
million and trillion times by the clad, each movement comprising of a straight line
and consequently because of such reflections, it acquires the shape of the optical
Fiber. So effectively, it is said to have been travelling along the Fiber. It changes its
direction only if there is a change in the dielectric medium as also illustrated by the
Tyndall’s experiment. To understand the propagation of light within an optical Fiber
it is necessary to take into account refractive index of the dielectric medium.
Refractive index of a medium is defined as the ratio of velocity of light in vacuum to
velocity of light in medium.
Velocity of light in vaccum
Refractive index =
Velocity of light in medium
Since, the velocity of light in any solid, transparent material is less than in vacuum the
refractive index of such material is always greater than 1.0. A ray of light travels
slowly in an optically dense medium than one that is less dense. Now, the direction
that the light approaches the boundary between the two materials is very important.
When a ray is incident on the interface between two dielectrics of differing refractive
indices, refraction occurs. The light is refracted and also partly reflected internally in
the same medium; which is referred as Partial Internal Reflection. It may be
observed that the ray approaching the interface is propagating in a dielectric of
refractive index n1 and is at an angle 1 to the normal at the surface of the interface.
If the dielectric on the other side of interface has a refractive index n2 which is less
than n1, then the refraction is such that the ray path in this lower index medium is at
angle 2 to the normal where 2 is greater than 1.

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Scientech 2501A Optical Fiber Communication

The angle of incidence 1and refraction 2 are related to each other and to refractive
indices of dielectrics by Snell's law of refraction which states that:
n
1sin1 n
2sin2
sin 1 n2
sin 2 n1

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Scientech 2501A Optical Fiber Communication

It is this change in refractive indices which causes the change in the path of the
incident ray as evident from the Snell’s law. Larger the change in the refractive
indices larger change in the direction of the incident ray. The ‘Sine’ of the angles will
be in the ratio of their refractive indices. As the angle of incident ray increases, the
angle of refraction also increases even faster and when the angle of refraction
becomes 90° thereafter, if the angle of incidence is increased a condition is arrived
where the incident ray is totally reflected in the same medium from where it has
emerged; this is referred as the total internal reflection.
Total Internal Reflection:
Since, the angle of refraction is always greater than the angle of incidence, when the
incident medium is denser than the refraction medium. Thus, the angle of refraction is
90° and the refracted ray emerges parallel to the interface between the dielectrics.
This is the limiting case of refraction and this angle of incidence is known as critical
angle c.
The value of critical angle is given by:
2= 90
1= c

Substituting this in the equation for Snell’s law gives

ns
1i n c=ns
2in9
0
n2
sin c=
n1

At angles of incidence greater than the critical angle the light is reflected back into the
originating dielectric medium. This behaviour of light is termed as Total Internal
Reflection.
Here, Angle of Incidence = Angle of Reflection

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Scientech 2501A Optical Fiber Communication

This is the mechanism by which light may be considered to propagate down an optical
fiber with low loss. Shown in next figure below illustrates the transmission of a light
ray in an optical fiber via a series of total internal reflection at the interface of the
silica core and slightly lower refractive index silica cladding.

The light ray shown in next figure is known as meridian ray as it passes through the
axis of the fiber core. It is generally used when illustrating the fundamental
transmission properties of optical fiber.
Acceptance Angle:
Since, only rays with an angle greater than critical angle at the core cladding interface
are transmitted by total internal reflection, it is clear that not all rays entering the fiber
core will continue to propagate down the length.

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Scientech 2501A Optical Fiber Communication

Shown in next figure illustrates two incident rays I and B. It may be observed that ray
‘I’ enters the fiber core at an angle i less than (conical half angle for the fiber
explained herein under) to the fiber axis and is refracted at the air- core interface
before transmission to the core- cladding interface at an angle more than the critical
angle c. This ray is totally internally reflected and propagated along the fiber. While
incident ray ‘B’ is incident into the fiber core at an angle b greater than a and will
be transmitted to the core- cladding interface at an angle less than c and will not be
totally internally reflected instead will be refracted into cladding and eventually lost
by the radiation. Thus, for rays to be transmitted by total internal reflection within the
fiber core they must be incident on the fiber core within an acceptance cone defined
by conical half angle a. Hence, a is the maximum angle to the axis at which light
may enter the fiber in order to be propagated and is referred to as the acceptance
angle for the fiber?
Here i < a < b

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Scientech 2501A Optical Fiber Communication

Numerical Aperture:
It gives the relationship between the acceptance angle and the refractive indices of the
three media involved viz. the core, the cladding and air.
Shown in next figure above i corresponds to i; when i approaches c; i
approaches a
By Snell's law of refraction:-
n
0sina n
1sin
(9
0 c
) {
whe
re c isth
ecr
itic
ala
ngle
}
n
1cosc
2 1
/2
n
1(
1sin
c )

2
n21 n
n
1(
1 2
)/2 {
ass
inc 2
}
n1 n
1
2 2
n
1 n2

This term is referred as numerical aperture of the Wave Guide – Optical Fiber.

22 1
/
2 22
N
u
m
er
i
c
al
Ap
er
t
ur
ens
i
0na(
n1n)
2 (
n
1 n
)
2

(
n
1n)
(
2n
1n
2)
Where,
n0 = Refractive index of air
n1 = Refractive index of core
n2 = Refractive index of cladding
The Numerical Aperture is a very useful measure of light collecting ability of a fiber.
It directly relates to the refractive indices of the core and cladding. As we observe
from the above equation, greater the absolute value of the indices of core and
cladding, greater the numerical aperture; similarly, greater the difference between the
refractive indices greater the numerical aperture. In accordance to the requirement of
the numerical aperture, the material for the core and cladding is chosen, keeping in
view the other parameters and requirements for transmission.

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Scientech 2501A Optical Fiber Communication

Advantages of FIBER Optic System

● Enormous Potential Band Width (BW) :
The information carrying capacity of a transmission system is directly
proportional to the carrier frequency of the transmitted signals.The optical
carrier frequency in the range 1013 to 1016 Hz. (generally near infrared around
1014 or 1015 Hz) yields a far greater potential transmission B.W. than metallic
cable system. (i.e. coaxial cable Bandwidth up to 500 MHz) or even millimetre
wave radio system, (i.e. system currently operating with modulation Bandwidth
of 700 MHz) . Thus the optical Fibers have enormous transmission bandwidths
and high data rate. Using wavelength division multiplexing operation, the data
rate or information carrying capacity of optical fibers is enhanced to many
orders of magnitude.At present the Bandwidth available to fiber system is not
fully utilized by modulation at several GHz over hundred km. and hundreds of
MHz over 300 Km with intervening electronics (repeaters) is possible.
Therefore, the information carrying capacity of optical fiber system has proved
far superior to best copper cable available, by comparison losses in coaxial cable
systems restrict. A much-enhanced Bandwidth utilization for an optical fiber can
be achieved by transmitting several optical signals each at different centre
wavelengths in parallel on the same fiber. This wavelength division multiplexed
operation particularly with dense packing of the optical wavelength (or fine
frequency spacing) offers potential information carrying capacity.
● Small size and weight :
Optical Fibers have very small diameter in the ranges from 10 micrometers to
50 micrometers. The space occupied by the fiber cable is negligibly small
compared to conventional electrical cables.Hence, when they are covered with
protective coatings they are far smaller & lighter. This is a tremendous boon
towards the alleviation of duct congestion in cities and allowing expansion of
signal transmission in mobiles e.g. aircrafts, ships etc.
● Electrical Isolation :
Optical Fibers are fabricated from glass or plastic polymers, they are electrical
insulators therefore they do not exhibit earth loop, interference problems,
electromagnetic wave or any high current lightening. This property makes them
suitable for communication in electrically hazardous environment as fiber create
no arcing or spark hazard at abrasions or short circuit & usually fiber do not
contain sufficient energy to ignite vapours or gases.It is also suitable in
explosive environment.

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Scientech 2501A Optical Fiber Communication

● Immunity to Interference and Cross talk :

Optical fibers form a dielectric wave-guide and therefore are free from Electro
Magnetic Interference (E.M.I), Radio Frequency Interference (R.F.I) or
switching transients. It is not susceptible to lightening striker if used overhead
rather than underground. Moreover it is easy to ensure that there is no optical
interference between fibers. Since optical interference among different Fibers is
not possible, cross talk is negligible even many Fibers are cabled together.
● Signal Security :
The light from optical fibers does not radiate significantly and therefore they
provide a high degree of signal security. Unlike in copper cables, a transmitted
signal cannot be drawn from a fiber without tampering it. Thus, the optical fiber
communication provides 100% signal security. A transmitted optical signal
cannot be obtained from a fiber in a non-invasive manner (i.e. without drawing
optical power form the fiber). In theory, any attempt to acquire a message signal
transmitted optically may be detected. This feature is obviously attractive for
military & banking.
● Low transmission loss:
Due to the usage of ultra low loss Fibers and the erbium doped silica Fibers as
optical amplifiers ,Optical fibers results in low attenuation or transmission loss
in comparison with the best copper conductor. It facilitates the implementation
of communication links with extremely wide repeater spacing thus reducing
both system cost and complexity. This quality along with already proven
modulation B W capability of fiber cable, it is used in long haul
telecommunication applications.Hence for long distance communication Fibers
of 0.002 dB/km are used. Thus the repeater spacing is more than 100 km.
● Potential Low Cost :
The glass that generally provides optical fiber transmission medium is made
from sand not a scarce resource. In comparison with copper conductors, optical
fiber offers low cost line communication. This is because many miles of optical
cable are easier and less expensive to install than the same amount of copper
wire or cable.
● Thinner:
Fiber optics is thinner than copper wire cables, so they will fit in smaller, more
crowded places. This is important for underground cable systems, like in cities,
where space needs to be shared with sewer pipes, power wires, and subway
systems.
● Non-flammable
Since fiber optics send light instead of electricity, fiber optics are non-
flammable. This means there is not a fire hazard. Fiber optics also do not cause
electric shocks, because they do not carry electricity.

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Scientech 2501A Optical Fiber Communication

● Ruggedness and flexibility

The Fiber cable can be easily bend or twisted without damaging it. Further the
fiber cables are superior than the copper cables in terms of handling, installation,
storage, transportation, maintenance, strength and durability.
● Low cost and availability
Since the Fibers are made of silica which is available in abundance. Hence, there
is no shortage of material and optical fibers offer the potential for low cost
communication.
● Reliability
The optical Fibers are made from silicon glass which does not undergo any
chemical reaction or corrosion. Its quality is not affected by external radiation.
Further due to its negligible attenuation and dispersion, optical fiber
communication has high reliability. All the above factors also tend to reduce the
expenditure on its maintenance.
The disadvantages of optical Fibers are:
● Price - Even though the raw material for making optical Fibers, sand, is
abundant and cheap, optical Fibers are still more expensive per metre than
copper. Although, one Fiber can carry many more signals than a single copper
cable and the large transmission distances mean that fewer expensive repeaters
are required.
● Fragility - Optical Fibers are more fragile than electrical wires.
● Affected by chemicals - The glass can be affected by various chemicals
including hydrogen gas (a problem in underwater cables.)
● Opaqueness - Despite extensive military use it is known that most Fibers
become opaque when exposed to radiation.
● Requires special skills - Optical Fibers cannot be joined together as a easily as
copper cable and requires additional training of personnel and expensive
precision splicing and measurement equipment.

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Scientech 2501A Optical Fiber Communication

The Optic Fiber:

The simplest Fiber optic cable consists of two concentric layers of transparent
materials. The inner portion the core transports the light, the outer covering (the
cladding) must have a lower refractive index than the core so the two of them are
made up of different materials.
To provide mechanical protection for the cladding an additional plastic layer; called
Primary Buffer is added. Some constructions of optic Fiber have additional layers of
buffers that are then referred to as Secondary Buffers. It is very important to note that
the whole Fiber-Core, Cladding & Primary Buffer is solid and the light is confined to
the core by the Total Internal Reflection due to the difference in the refractive index
of the core as compared to that of cladding.

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Scientech 2501A Optical Fiber Communication

Single Mode versus Multi Mode:

As we have already seen that there are particular angles of propagation defined by
cone of acceptance, which can be transmitted down the optic fiber. At these angles,
the electromagnetic wave that the light can set up a number of completes patterns
across the fiber. The number of complete patterns called Modes depends on the
dimensions of the optic fiber core. There are essentially two different types of fiber
optic transmission schemes in use viz.
● Single Mode
● Multi Mode
Single Mode:
As the name suggests the single mode cable is able to propagate only one mode
(Electromagnetic wave). This is used in long distance and/or, high-speed
communication. It is beneficial over long distances since it completely eliminates a
problem known as inter modal Dispersion associated with Multimode cables. All our
long distance telephone conversations are now carried by single mode optic fiber
system over at least some part of the route.

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Scientech 2501A Optical Fiber Communication

Multi Mode:
The term multimode means that the diameter of the fiber optic core is large enough to
propagate more than one mode (Electro Magnetic Wave).
Because of the multiple modes the pulse that is transmitted down the fiber tends to
become stretched over distance this is referred to as dispersion & has the effect of
reducing the available bandwidth. These are typically used in applications such as
LAN (Local Area Networks) & FDDI (Fiber Distributed Area Interface)

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Scientech 2501A Optical Fiber Communication

Optical Fiber Index Profile

Index profile is the refractive index distribution across the core and the cladding of a
fiber. Some optical fiber has a step index profile, in which the core has one uniformly
distributed index and the cladding has a lower uniformly distributed index. Other
optical fiber has a graded index profile, in which refractive index varies gradually as a
function of radial distance from the fiber centre. Graded-index profiles include power-
law index profiles and parabolic index profiles.
Step Index And Graded Index Fibers:
The first type of fiber optic cable put to use was called step index. In this design, the
cladding has a different index of refraction than the core. The light bounces off the
side and is reflected back into the fiber core. The problem with this design is that the
reflected light must travel a slightly longer distance, than that which travels down the
centre of the fiber, thus limiting the maximum transmission rate. This design was
improved with the use of Graded index fiber. In this design, the index of refraction
decreases in proportion to the distance away from the centre of the fiber core. The
light moves more quickly in the outer portion thus compensating for the additional
distance. The change in index has the effect of bending. The light reflects back
towards the core. This change increases the transmission capacity by a reasonable
factor. In the newest single mode design, the diameter of the fiber core is so small that
all the light travels in a straight line. Even the latest fiber optic facility in use today
uses less than 5% of the maximum theoretical capacity of a single mode fiber.

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Scientech 2501A Optical Fiber Communication

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Scientech 2501A Optical Fiber Communication

Some of the optical fibers in use are:

● Multimode step index fibers.
● Multimode graded index fibers.
● Single mode step index fibers.
● Plastic - clad fibers.
● All plastic fibers.
Dimensions of fiber optic cables are written as a ratio e.g. a cable with cladding
diameter of 125 microns and fiber core diameter of 62.5 or 50 microns will be
referred to as 62.5 /125 or 50 / 125 fibers. That is if the diameter of the core is Dcr and
the diameter of the clad is Dcd both in microns (1 micron = 10- 6 meters), then the
dimensions of the Fiber optic cable will be denoted as Dcr/ Dcd.

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Scientech 2501A Optical Fiber Communication

Choice of Operating Frequency:

Once we had the Laser and the new optic fiber available, everything was in place for a
significant upsurge in communications. This resulted in two driving forces: one
towards the ability to send more data faster and secondly to send the data to greater
distances without being re-amplified.
More Data Faster:
As the transmission rate of data is increased, the required bandwidth increases and
this can be best accommodated by increasing the carrier frequency. This premise has
stood us in good stead over many years. The speech and poor quality music
transmissions on the medium frequency, AM radio, gives way to the higher frequency
of FM radios which accommodate the increased bandwidth necessary for improved
music quality. When television required even higher data rates, we responded by
moving to even higher frequencies. These previous experience rather suggested that
the light used for fiber optic communications should be of the highest frequency
possible. But there was a surprise in store!
Lower Frequencies Mean Lower Losses:
The first experiments used visible light of different colours (frequencies). As the
losses were measured, we found that the higher frequencies caused more losses.
The losses actually increased by the 4th power of the frequency. This means that a
tripling of the frequency would result in the losses increasing by 34 or 81 times. We
therefore have two conflicting influences:
High frequency = High Data Rates
Low frequency = Long Ranges
At the moment, long distance communication is more important than achieving the
ultimate in data transmission rates. Therefore in most real installations, we tend to go
for the relatively low frequencies of infrared light that is just below the visible
spectrum.

26
Scientech 2501A Optical Fiber Communication

Fiber Windows:
We now have an infrared range between 800 nm – 1700 nm (1 nanometre = 10-9
meter) with one part of it around 1380 nm that is to be avoided due to high losses
because of Hydroxyl Ion Absorption as is clear from the graph optical wavelength
versus losses per kilometre (dB) . It seemed sensible to agree on standard wavelengths
so that equipment from different manufacturers can be made compatible.

This has resulted in three standard wavelength slabs called windows. The windows
were really the result of looking at the available light sources. Some wavelengths of
LED and LASER light are easier and less expensive than others to produce. The
design and manufacture of the optic fiber is then optimized for these frequencies.
Note: The infrared light is very dangerous to eyes which can cause irreversible
damages and since it is invisible, care should be taken to ensure that the optic fiber is
not live.

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Scientech 2501A Optical Fiber Communication

Losses in Optic Fiber:

● Attenuation
● Material Absorption Losses
● Linear Scattering Losses
Ray Leigh Scatter
Mie Scattering
● Non Linear Scattering
● Micro Bending and Macro Bending
● Dispersion
Inter modal Dispersion
Intra modal Dispersion
● Attenuation :
Transmission of light is not 100 % efficient. Some photons of light are lost,
causing attenuation of signal. Several mechanisms are involved, including
absorption by materials within the fiber, scattering of light out of the core
caused by environmental factors. The degree of attenuation depends on the
wavelength of light transmitted. Attenuation measures the reduction in signal
strength by comparing output power with input power. Measurements are made
in decibels (dB). It is defined as: -
Pi
dB loss = 10 log 10 P
o

28
Scientech 2501A Optical Fiber Communication

● Material Absorption Losses :

It is a loss mechanism related to the material composition and fabrication
process of the fiber that result in the dissipation of some of the transmitted
optical power as heat in wave-guide. The absorption of light may be intrinsic
(caused by one or more major components of glass) or extrinsic (caused by
impurities within the glass).
● Linear Scattering Losses :
Linear scattering mechanisms cause the transfer of some or all of the optical
power contained within one propagating mode to be transferred linearly
(proportionally) into a different mode. This process tends to result in attenuation
of the transmitted light as the transfer may be to a leaky or radiation mode that
doesn't continue to propagate within the fiber core, but is radiated from the fiber.
It is mainly of two types.
Ray Leigh Scattering
Mie Scattering

29
Scientech 2501A Optical Fiber Communication

Ray Leigh Scattering:

When the infrared light strikes a very-very small place where the materials in
the glass are imperfectly mixed, this gives rise to localized changes in the
refractive index resulting in the light being scattered in all directions. Some of
the light escapes the optic fiber, some continues in the correct direction and
some is returned towards the light source. This is called backscatter.

Mie Scattering:
These result from the non - perfect cylindrical structure of the wave-guide. It
may be the caused by the imperfections such as irregularities in the core
cladding interface core, cladding refractive index difference along the fiber
length, diameter fluctuations, strains and bubbles. The scattering created by such
in homogeneities is mainly in the forward direction.
● Non Linear Scattering :
Optical wave-guide does not behave linearly, several non-linear effects occur,
which in the case of scattering cause disproportionate attenuation usually at high
optical power level. This non-linear scattering causes the optical power from
one mode to be transferred in either the forward or backward direction to the
same, or other modes at different frequency. It depends critically upon the
optical power density within the fiber and hence only becomes significant above
threshold power levels.
● Micro Bending and Macro Bending :
A problem that often occurs in cabling of the optical fiber is the twisting of the
fiber core axis on a microscopic scale within the cable form. This phenomenon,
known as micro bending result from small lateral forces exerted on the fiber
during the cabling process and it causes losses due to radiation in both
multimode and single mode fiber.

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Scientech 2501A Optical Fiber Communication

● Macro bends :
The light propagates down the optic fiber solely because the incident angle
exceeds the critical angle. If a sharp bend occurs, the normal and the critical
angle move round with the fiber. The incident ray continues in a straight line
and it finds itself approaching the core - cladding boundary at an angle less than
the critical angle and much of light is able to escape.

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Scientech 2501A Optical Fiber Communication

● Dispersion :
When an electrical pulse energizes a LASER, it launches a short flash or light
along the optic fiber. It is an unfortunate fact that the light burst becomes longer
as it moves along the fiber optic cable. The light spreads out. This effect is
called 'Dispersion', shown in next figure the light pulse shown before and after it
has travelled through the cable.

It is going to limit how fast we can send data - how many bits per second we can
transmit through a fiber optic link. In fact it is the main limit to the data
transmission rate for long distance communication system.
If we send flashes of Laser light down a long link in which dispersion is a
problem, the flashes will merge at the far end and the ON/OFF states will not be
distinguished by the receiver. Over a given transmission path, there are only two
remedies. Firstly, we could reduce the transmission rate so that even allowing
for the spreading effect of the dispersion; the ON-OFF states are still clearly
separated. This is not a very exciting solution and would clash with one of the
main reasons for using optic fiber.
There are two types of Dispersion:
Inter modal Dispersion
Intra modal Dispersion

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Scientech 2501A Optical Fiber Communication

Inter modal Dispersion:

You will recall that, to be propagated down the core of the optic fiber, the light
must enter at an angle greater than the critical angle. Let us consider just two
such rays of light as they travel along a section of optic fiber.

Ray ‘A’ will reach the far end before Ray ‘B’ since it is travelling a shorter
distance. Assuming that rays A and B are part of the same pulse of light and
start at the same time, we can now see how the spreading of the pulses can
occur. Each and every ray being propagated at its own angle will arrive at
slightly different times at the far end. This spreading effect will occur all along
the fiber so it is also important to appreciate that the longer the optic fiber, the
greater the dispersion. Transmission rates that are actually possible on an optic
fiber therefore depend in its length. In practice, there are only particular angles
of propagation that can be transmitted down the optic fiber.
Intra modal Dispersion:
This form of dispersion occurs in both multi mode and single mode optic fibers.
It is only really significant in single mode usage since, being very slight; it is
completely swamped by the inter-modal dispersion in the multimode case. The
cause is simple enough - the refractive index of material is determined to some
extent by the wavelength of the light source. Can you see how this causes
dispersion? A change in refractive index will change the speed of that particular
wavelength of light. Now if your light source produces different wavelengths at
the same time, we will have components of the transmitted light pulse travelling
at the same time, we will have components of the transmitted light pulse
travelling at different speeds. The total package of light will spread out - hence
the dispersion.
● Cure for Inter modal Dispersion :
A large core diameter means many modes and severe inter modal dispersion.
The cure for this type of dispersion is quite simple. Reduce the core size; the
number of modes decreases and the inter-modal dispersion is reduced. We can
do better than just reducing the inter-modal dispersion, we can completely
eliminate it. Simply make the core so small that only one mode is propagated. A
single ray cannot possibly go at two different speeds so inter modal dispersion
cannot occur. In practice the core is reduced to about 9 m (micron). The optic
fiber that now carries only a single mode is now referred to as a 'single mode
fiber'. Single mode fiber is used for all long distance and/or high-speed
communications. All long distance telephone conversations are now carried by
single mode fiber optic systems over some parts of the route. The larger core
optic fibers for short and medium distances carry many modes and are called
'Multimode'.

33
Scientech 2501A Optical Fiber Communication

● The Cure for Intra modal Dispersion :

The cure is apparently so simple; use a light source that emits only one
wavelength of light. Unfortunately, it has not yet been invented. Our light
sources in current use are the LED and the LASER. Study shown in next and
decide which of the two would cause the lesser amount of Intra modal
Dispersion.

The LASER would cause less intra modal dispersion because its light is more
concentrated around the central wavelength. The spread of wavelength measured
between the points where the power output falls to half of the peak power is called the
spectral width. Some LASERS have spectral widths as low as 0.1 nm (nanometre).
The low spectral width together with its high power and fast switching makes the
LASER first choice for long distance communications using single mode optic fiber.
Also there are some losses due to coupling in between the fibers at LED and photo
detector ends.
Applications of Macro bends:
A Live Fiber Detector:
Here is the problem long distance fiber optic systems employ powerful LASER
operating in the infrared region of the spectrum. This infrared light has two properties
that are very significant to the engineers and technicians working on the system. We
have various pieces of test equipment that can be used to check the system. The' live '
fiber detector is able to find which fibers are carrying data in most day to day checks,
but read the instruction manual first to ensure that the instrument is suitable for the
type of optic fiber you are checking.

34
Scientech 2501A Optical Fiber Communication

This device has a pair of spring-loaded jaws. The fiber under test is slipped in
between them and when the jaws close it will cause the fiber to be bent sufficiently to
cause a macro bend. The escaping light can be detected by the photocell and used to
activate the LED indicator. One flaw in the system is that it relies on the buffer being
transparent to the infrared light.
The Optical Time Domain Reflectometer (OTDR):
The OTDR is a measuring instrument that uses backscatter. It is the most versatile
piece of test equipment that we have for making measurements on fiber optic systems.
It provides us with two different measurements:
● It can measure the magnitude of any losses that occur along optic fiber.
● It can measure distance along the optic fiber.

35
Scientech 2501A Optical Fiber Communication

Losses:
As the light moves along the optic fiber, the light intensity is attenuated by the losses
in the optic fiber and so the reflections returned to the OTDR receiver become
weaker. Measurement of the amplitude of the returned signals tells us the optic fiber
loss in dB/Km. if a macro bend has occurred, it would show up as a drop in the signal
level at a particular point. (If the optic fiber has been cut, a connector should be fitted
in such a way that end face of the glass causes a reflection of energy. It is also usual
for this to occur at the extreme end of the optic fiber. This cause a localized increase
in energy returned to the Optical Time Domain Reflectometer (OTDR). This
reflection called as Fresnel (the ‘s’ is not pronounced) reflection shown up as a small
spike on the display. There is always a Fresnel Reflection at the start of the fiber due
to the connector on the front panel of the OTDR.
Distance:
We obtain timing information by starting the display and the pulse generator at the
same instant. This is achieved by the synchronizing pulse that switches on both the
LASER and the receiver at the same instant. If we know how long it takes for the
backscatter light to return to the OTDR then we only have to know how fast the
infrared light is travelling along the optic fiber to be able to calculate how far the light
has travelled some light returns after say, 500 ns, it follows that it has travelled to a
total of 100 meters. This represents 50 meters out along the optic fiber and 50 meters
back. You will remember that the actual speed of propagation is determined by the
refractive index of the core of the optic fiber.
Speed of propagation = speed of light in free space / refractive index of the core
(The refractive index of the optic fiber being tested must be punched in to the OTDR
otherwise all the distance will miscalculated. The value of the refractive index is
coated by the manufacturer).
The synchronizing pulse simply provides a start to the generator and to the display
circuits to allow them to determine the travel-time of the laser light and the
backscatter.

36
Scientech 2501A Optical Fiber Communication

Shows in next figure Fiber Optic System together with its appearance on OTDR
screen. Notice that both the macro bends and fusion splices are shown as a sudden
loss of power at a particular point. Indeed, it is not possible to distinguish between
macro bed and a fusion splice just by observing the OTDR display. It just shows a
localized loss. The loss may appear as a vertical drop or a sloping line depending
upon the speed at which the screen being scanned on the OTDR. The connector has a
similar loss but it also has a Fresnel reflection. Typical value of losses:
Fusion splice - 0.05 dB
Connector - 0.2 dB
Macro bend: 0 dB to more than 8 dB depending on the severity of the macro bend.
Two Other Applications of Back scatter.

37
Scientech 2501A Optical Fiber Communication

Distributive Temperature Sensing (DTS):

The amount of backscatter occurring in an optic fiber is dependent upon the
manufacture of the optic fiber, the optic window used, and also upon the temperature
of the optic fiber. Now, when we find a characteristic of the optic fiber that depends
on the temperature, it is but a small step away from using the effect to measure
temperatures. This new technique is called Distributive Temperature Sensing (DTS).
Basically it is an optic fiber connected to equipment operating just like an OTDR that
is then passed through the areas to be measured. If it passes through a refrigerator
(minimum temperature of 190 C or 310 F), shown in next figure e.g. the trace on the
OTDR will show the backscatter level falling to a level dependent upon the
temperature in the refrigerator. Similarly, a heated area (maximum temperature 460 C
or 860 F) would return a higher level of backscatter.
Security:
You will recall that one of the advantages of the fiber optic system is the high level of
security offered. We know however, that a macro bend would allow the light to
escape and hence the data to be copied. An OTDR monitoring the line would
immediately detect the power loss of the macro bend and be able to measure its
distance along the optic fiber to an accuracy of approximately 0.1 meters (4 inches)
the same immediate detection would occur as with the security matting shown in next
figure.

38
Scientech 2501A Optical Fiber Communication

Fiber optic links:

Fiber optic links can be used for transmission of digital as well as analog signals.
Basically a fiber optic link contains three main elements, a transmitter, an optical fiber
and a receiver. The transmitter module takes the input signal in electrical form and
then transforms it into optical (light) energy containing the same information. The
optical fiber is the medium, which takes the energy to the receiver. At the receiver
light is converted back into electrical form with the same pattern as originally fed to
the transmitter.
Transmitter:
Fiber optic transmitters are typically composed of a buffer, driver and optical source.
The buffer provides both an electrical connection and isolation between the
transmitter & the electrical system supplying the data. The driver provides electrical
power to the optical source. Finally, the optical source converts the electrical current
to the light energy with the same pattern. Commonly used optical sources are light
emitting diodes (LED) and LASER beams. Simple LED circuits, for digital and
analog transmissions are shown below.

39
Scientech 2501A Optical Fiber Communication

Shown in next figure Tran conductance drive circuits for analog transmission-
common emitter configuration. The transmitter section comprises of:
● Function Generator
● Frequency Modulator &
● Pulse Width Modulator Block.
The Function Generator generates the input signals that are going to be used as
information to transmit through the fiber optic link. The output voltage available is 1
KHz sinusoidal signal of adjustable amplitude, and fixed amplitude 1 KHz square
wave signal. The modulator section accepts the information signal and converts it into
suitable form for transmission through the fiber optic link.
The Fiber Optic Link:
Emitter and Detector circuit on board form the fiber optic link. This section provides
the light source for the optic fiber and the light detector at the far end of the fiber optic
links. The optic fiber plugs into the connectors provided in this part of the board. Two
separate links are provided.
The Receiver:
The Comparator circuit, Low Pass Filter, Phase Locked Loop, AC Amplifier Circuits
form receiver on the board. It is able to undo the modulation process in order to
recover the original information signal. In this experiment the TechBook board is
used to illustrate One-Way communication between digital transmitter and receiver
circuits.

40
Scientech 2501A Optical Fiber Communication

Shown in next figure a simple drive circuit for binary digital transmission consisting
of a common emitter-saturating switch.
Modulation:
In order to transmit information via an optical fiber communication system it is
necessary to modulate a property of the light with the information signal. This
property may be intensity, frequency, and phase with either digital or analog signals.
The choices are indicated by the characteristics of optical fiber, the available optical
sources and detectors, and considerations of the overall system.
Intensity Modulation:
In this system the information signal is used to control the Intensity of the source. At
the far end, the variation in the amplitude of the received signal is used to recover the
original information signal.

The audio input signal is used to control the current through an LED which in turn
controls the light output. The light is conveyed to the detector 1 circuit by optic fiber.
The detector is a phototransistor that converts the incoming light to a small current
which flows through a series resistor. This gives rise to a voltage whose amplitude is
controlled by the received light intensity. The voltage is now amplified within the
detector circuit and if necessary, amplified further by amplifier circuit.

41
Scientech 2501A Optical Fiber Communication

The Analog Bias Voltage:

There are two problems using amplitude modulation with an analog signal. The first is
to do with the signal itself.

If you glance at the shown in next figure you will see that analog wave form moves
positive & negative of the zero line. The second problem is that it is the shape of the
waveform that carries the information. Ideally the emitter characteristic would be a
straight line. Even so we would lose the negative going half cycles as shown in next
figure below:

The answer is to superimpose the sinusoidal signal on positive voltage called the bias
voltage so that both halves of the incoming signal have an effect on the light intensity.
The combination of linear characteristic would be ideal but the real characteristic is
not completely straight. However it does have a straight section that we can use if we
employ a suitable value of bias voltage. Shown in next figure ideal and practical
situations.

42
Scientech 2501A Optical Fiber Communication

Digital Modulation:
With digital modulation, discrete changes in light intensity are obtained (i.e. ‘On-Off’
pulses) shown in next figure a block schematic of a typical digital optical fiber link.

Initially, input digital signal from the information source is suitably encoded for
optical transmission. The LED drive circuit directly modulates the intensity of the
light with encoded digital signal. Hence, a digital optical signal is launched into the
optical fiber cable. An amplifier to provide gain follows the phototransistor used as
detector. Finally, the signal obtained is decoded to give the original digital
information.

43
Scientech 2501A Optical Fiber Communication

Digital Bias Voltage:

In case of a digital signal the only information which needs to be conveyed is the ’On’
state and ‘Off’ state. The digital Input signal is entirely positive going as shown in
next figure.

So, there is no negative part of the signal to be lost and further more any distortion
due to non-linearity of the characteristic is of no importance; all we need to know is
whether the signal is ‘On’ or ‘Off’. There is no need therefore to generate a bias
voltage. When amplitude modulation is used with a digital input we employ a
comparator at the receiving end of the fiber to make the waveform square again called
'cleaning it up'.

44
Scientech 2501A Optical Fiber Communication

Frequency Modulation:
In the traditional form of FM the carrier frequency is changed or modulated by the
amplitude of the analog signal. In a fiber optic system this is not feasible since both
our light sources; the LED and the LASER are fixed frequency devices. In fiber optic
systems FM is achieved by using the original analog input signal to vary the
frequency of a train of digital pulses.

Frequency Modulation

A circuit called Voltage Controlled Oscillator usually abbreviated as VCO achieves

this. The digital pulses are communicated through the optic fiber and squared up at
the receiver by a comparator in the same way as it was in amplitude modulation
system. At this point, we convert the digital train back to the original analog signal by
means of the Phase Locked Loop Detector (PLL). The PLL circuit performs a very
simple function. It monitors an incoming signal and produces a DC Voltage output. If
the input frequency increases, the DC voltage increases. If the frequency decreases,
the DC voltage decreases in this way the original analog signal is recovered. The
output of the PLL contains many unwanted frequency components. A Low Pass Filter
removes these and then finally the signal is amplified to the desired level.

45
Scientech 2501A Optical Fiber Communication

Pulse width modulation:

Pulse width modulation (PWM) is an alternative to frequency modulation. They are
both digital transmission. In FM, you will remember, the incoming analog signal is
used to change the frequency of the digital stream. In pulse width modulation the
amplitude of the analog signal to be transmitted as the changes in the width of the
pulse. It is an extremely simple system of modulation. Assume an input signal at zero
volts.

The digital stream and the average voltage level would be as shown in next figure.

Pulse Width Modulation

46
Scientech 2501A Optical Fiber Communication

If the input voltage moves to a positive value, the pulse width will increase and since
the waveform is ‘On’ longer than it is ‘Off’ the average value increases. Similarly, if
the input signal goes negative the width of the pulse will decrease. The average value
of the digital voltage now decreases. You will now appreciate that the average voltage
level is increasing and decreasing in accordance with the input voltage. At the far end
of the transmission system the digital pulses are cleaned up by the comparator and
then simply passed through a low pass filter. The filter removes the square waves but
the average level remains to form the output signal. At this stage, the output signal is
increasing and decreasing in step with the input, but you will remember that the OV
input signal produced a DC level at the output. This DC level must now be removed.
We do this by means of blocking capacitors at the input to the final amplifier.
Recommended Testing Instruments for Experiments:
Scientech Oscilloscope

47
Scientech 2501A Optical Fiber Communication

Experiment 1
Objective: Study of 650 nm Fiber Optic Analog link.
In this experiment you will study the relationship between the input signal and
received signal.
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are OFF.
Make the connections as shown in next figure
 Connect the Function Generator 1 KHz sine wave output to emitter input.

48
Scientech 2501A Optical Fiber Communication

 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to AC amplifier input.
Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Switch ‘On’ the Power Supply of the TechBook and Oscilloscope.
● Observe the input to emitter with the output from AC amplifier on Oscilloscope.
Observation:
Observe the waveforms as shown below.
Both the input and output waveforms are same.

Input to Emitter circuit Input to Emitter LED

(CH1-2V/div; TB- 0.5mS) (CH1-2V/div; TB- 0.5mS)

Output of Detector circuit Output of AC Amplifier circuit

(CH1-0.2V/div; TB- 0.5mS) (CH1-2V/div; TB- 0.5mS)
Questions:
● What is meant by index profile?
● What is the drawback of multimode Fibers?
● What is Fiber optics?

49
Scientech 2501A Optical Fiber Communication

Experiment 2
Objective: Study of 650 nm Fiber Optic Digital Link.
In this experiment you will study the relationship between the input signal and
received signal.
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are OFF.
Make the connections as shown in next figure
Connect the Function Generator 1 KHz square wave output to emitter
input
Connect the fiber optic cable between emitter output and detector input.
Connect the detector output to comparator input.

50
Scientech 2501A Optical Fiber Communication

Put the mode switch SW1 to Digital to drive the emitter in digital mode.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
● Monitor both the inputs of comparator. Slowly adjust the comparator bias
potentiometer, until DC level on the input lies mid-way between the high and
low level of the signal on the positive input.
Observations:
Observe the waveforms as shown below.
Both the input and output waveforms are same.

Input to Emitter circuit Input to Emitter LED

(CH1-5V/div; TB- 0.5mS) (CH1-5V/div; TB- 0.5mS)

Output of Detector circuit Output of Comparator circuit

(CH1-2V/div; TB- 0.5mS) (CH1-5V/div; TB- 0.5mS)
Questions:
● Why single mode Fibers are used for long distance transmission?
● What is optical Fiber?
● What is step index profile?

51
Scientech 2501A Optical Fiber Communication

Experiment 3
Objective: To obtain Intensity Modulation of the Analog Signal, transmit it over a
fiber optic cable and demodulate the same at the receiver end to retrieve the original
signal.
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

52
Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the Function Generator output marked 1 KHz sine wave to input
of emitter.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to input of the AC amplifier.
Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Turn the 1 KHz potentiometer in Function Generator block to fully clockwise
(maximum amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
With the help of dual trace Oscilloscope observe the input signal at emitter.
Also, observe the output from the detector. It should carry a smaller version of
the original 1 KHz sine wave, illustrating that the modulated light beam has
been reconverted back into an electrical signal.
The output from detector is further amplified by AC amplifier this amplifier
increases the amplitude of the received signal and also removes the DC
component, which is present at detector output. Monitor the output of Amplifier
and adjust the gain adjust potentiometer until the monitored signal has the same
amplitude as that applied to emitter input.
● While monitoring the output of Amplifier change the amplitude of modulating
sine wave by varying the 1 KHz potentiometer in the Function Generator block.
Note that as expected, the amplitude of the receiver output signal varies.

53
Scientech 2501A Optical Fiber Communication

Observation:
Observe the waveforms as shown below.

Input to Emitter circuit Input to Emitter LED

(CH1-2V/div; TB- 0.5mS) (CH1-2V/div; TB- 0.5mS)

Output of Detector circuit Output of AC Amplifier circuit

(CH1-0.2V/div; TB- 0.5mS) (CH1-2V/div; TB- 0.5mS)

Questions:
● What is the function of transmitter, Optical Fiber and receiver?
● Where Fiber optics links can be used?
● What is spectral width?

54
Scientech 2501A Optical Fiber Communication

Experiment 4
Objective: To obtain Intensity Modulation of the Digital Signal, transmit it over a
fiber optic cable and demodulate the same at the receiver end to retrieve the original
signal.
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

55
Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the 1 KHz square wave socket in Function Generator block to
emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to comparator input.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode. This
ensures that signal applied to the driver input cause the emitter LED to switch
quickly between ‘On’ & ‘Off’ states.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Examine the input to emitter on an Oscilloscope this 1 KHz square wave is now
being used to amplitude modulates emitter LED.
Examine the output of detector. This should carry a smaller version of original 1
KHz square wave illustrating that the modulated light beam has been
reconverted into an electrical signal.
Monitor inputs of comparator and slowly adjust the comparator bias
potentiometer until the DC level on the negative input lies mid-way between the
high & low level of the signal on the positive input. This DC level is
comparator's threshold level.
Examine the output of comparator. Note that the original digital modulating
signal has been reconstructed at the receiver.
● Once again carefully flex the fiber optic cable; we can see that there is no
change in output on bending the fiber. The output amplitude is now independent
of the bend radius of the cable and that of length of cable, provided that detector
output signal is large enough to cross the comparator threshold level. This
illustrates one of the advantages of amplitude modulation of a light beam by
digital rather than analog means. Also non-linear ties within the emitter LED &
phototransistor causing distortion of the signal at the receiver output are the
disadvantages associated with amplitude modulating a light source by analog
means. Linearity is not a problem if the light beam is switched ‘On’ & ‘Off’
with a digital signal, since the detector output is simply squared up by a
comparator circuit. To overcome problems associated with amplitude
modulation of a light beam by analog means, analog signals are often used to
vary or modulate some characteristic of a digital signal (e.g. frequency or pulse
width.). The digital signal being used to switch the light beam ‘On’ & ‘Off’ The
next two experiments illustrate how an analog signal can be used to modulate
two specific characteristics of a digital signal.

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Observations:
Observe the waveforms as shown below.
Both the input and output waveforms are same.

Input to Emitter circuit Input to Emitter LED

(CH1-5V/div; TB- 0.5mS) (CH1-5V/div; TB- 0.5mS)

Output of Detector circuit Output of Comparator circuit

(CH1-2V/div; TB- 0.5mS) (CH1-5V/div; TB- 0.5mS)

Questions:
● What is intensity modulation?
● What is the function of LASER?
● How the modulated signal is detected?

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Experiment 5
Objective: Study of Frequency Modulation (FM)
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Make the connections as shown in next figure
 Connect the Function Generator 1 KHz sine wave signal to frequency
modulator input.
 Connect the frequency modulator output to the emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Detector output to comparator input.
 Comparator output to the PLL detector input.

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 PLL detector output to the Low Pass Filter input.

 Low Pass Filter output to AC Amplifier input.
Put the mode switch SW1 to Digital to drive the emitter in digital mode. This
ensures that fast changing digital signal applied to the drivers input causes the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in the Function Generator block to fully anti-
clockwise (zero amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Monitor the output of the voltage controlled oscillator (VCO) in the frequency
modulator block. Note that the frequency of this digital signal is at present
constant, since the modulating 1 KHz Sine wave has zero amplitude.
Examine the output of the detector and check that the transmitted digital pulses
are successfully detected at the receiver.
With the help of dual trace Oscilloscope monitor both inputs to comparator.
Now adjust the bias potentiometer until the bias input is halfway between the
top and bottom of the square wave. You will remember that the function of the
comparator is to ‘clean up’ the square wave after its transmission through the
fiber optic link.
The output of comparator drives the input of the PLL detector, which produces a
signal whose average level is proportional to the frequency of the digital stream.
This average level is then extracted by low pass filter and amplified by AC
amplifier to produce the original analog signal at the amplifiers output. Examine
note that the output voltage is zero. This is expected since there is currently no
modulating voltage at the transmitter.
While monitoring the input to the frequency modulator block and the output
from AC amplifier turn the 1 KHz potentiometer to its fully clockwise
maximum amplitude position. Note that the modulating 1 KHz signal now
appears at the amplifiers output. If necessary, adjust the amplifiers gain adjust
potentiometer until the two monitored signal are equal in amplitude.
● In order to fully understand how this frequency modulation transmitter/ receiver
system works, examine the inputs and outputs of all functional blocks within the
system, using an Oscilloscope.

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Observations:
Observe the waveforms as shown below.

Frequency Modulator output(without input) Frequency Modulator output(with input)

(CH1-2V/div; TB- 20uS) (CH1-2V/div; TB- 20uS)

Input to Emitter LED Output of Detector circuit

(CH1-5V/div; TB- 20uS) (CH1-5V/div; TB- 20uS)

Output of Comparator circuit Output of PLL Detector

(CH1-5V/div; TB- 20uS) (CH1-1V/div; TB- 20uS)

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Output of LPF circuit Output of AC Amplifier circuit

(CH1-1V/div; TB- 0.5mS) (CH1-5V/div; TB- 0.5mS)
Questions:
● How the FM signal is generated?
● What are the various detection techniques of FM signals?
● Why FM is used for short distance communication?

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Experiment 6
Objective: Study of Pulse Width Modulation
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are set to off.
Make the connections as shown in next figure
 Connect Function Generator 1 KHz sine wave signal to the Pulse Width
Modulator input.
 Pulse width modulator output to emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Detector output to comparator input.
 Comparator output to the LPF detector input.

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 LPF output to AC amplifier input.

Put the mode switch SW1 digital to drive the emitter in digital mode. This
ensures that fast changing digital signals applied to the driver input cause the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in Function Generator block to fully
anticlockwise (zero amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Monitor the output of the pulse width modulator. Note that the pulse width of
this digital signal is at present constant, since the modulating 1 KHz sine wave
has zero amplitude.
Examine the output of the detector and check that the transmitted digital pulses
are successfully detected at the receiver.
Monitor both inputs comparator and if necessary, slowly adjust the comparator
bias potentiometer, until the DC level on the negative input lies mid-way
between the high and low level of the signal on the positive input.
The average level of comparators output is extracted by LPF and then amplified
by AC amplifier, which also removes the DC off set. Since the average level of
the comparator output is proportional to the pulse width, the original analog
signal appears at the amplifiers output. Examine and note that the output voltage
is zero. This is expected since there is currently no modulating voltage at the
transmitter.
While monitoring the input to the pulse width modulator block and the output
from AC amplifier turn the 1 KHz potentiometer to its fully clockwise
(maximum amplitude position.). Note that the modulating 1 KHz signal now
appears at the amplifier output. If necessary, adjust the amplifier gain adjust
potentiometer until the two monitored signals are equal in amplitude.
● In order to fully understand how this pulse width modulation transmitter/
receiver system works, examine the inputs and outputs of all functional blocks
within the system using an Oscilloscope.

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Observations:
Observe the waveforms as shown below.

PWM output (without input) PWM output (with input)

(CH1-2V/div; TB- 10uS) (CH1-2V/div; TB- 10uS)

Input and output of PWM in Dual mode Output of Photo Detector

(CH1/CH2 - 2V/div; TB- 50uS) (CH1-0.1V/div; TB- 20uS)

Output of Detector circuit Output of Comparator circuit

(CH1-1V/div; TB- 20uS) (CH1-2V/div; TB- 20uS)

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Output of LPF circuit Output of AC Amplifier circuit

(CH1-2V/div; TB- 0.5mS) (CH1-2V/div; TB- 0.5mS)

Questions:
● What is PWM?
● What is the advantage of using PWM in communication systems?
● What is the function of comparator circuit?

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Experiment 7
Objective: Measurement of Propagation or Attenuation Loss in the optical fiber
Equipments Required:
● Scientech 2501A TechBook with Power Supply Cord
● Optical Fiber Cable
● Scientech Oscilloscope with necessary connecting probe
Connection Diagram:

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Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the Function Generator 1 KHz sine wave output to emitter input.
 Connect 0.5 m optic fiber between emitter output and detector input.
 Connect Detector output to amplifier input.
Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Set the Oscilloscope channel 1 to 0.5 V/ Div and adjust 4-6 div amplitude by
using X 1 probe with the help of variable potentiometer in Function Generator
block at input of emitter.
Observe the output signal from detector on Oscilloscope.
Adjust the amplitude of the received signal as that of transmitted one with the
help of gain adjusts pot in AC amplifier block. Note this amplitude and name it
V1.
Now replace the previous fiber optic cable with 1 m cable without disturbing
any previous setting.
Measure the amplitude at the receiver side again at output of amplifier. Note this
value end name it V 2 . Calculate the propagation (attenuation) loss with the help
of following formula.

V1 - (L1+L2)
e
V2
Where
= loss in nepers / meter
1 nepers = 8.686 dB
L1 = length of shorter cable (0.5 m)
L2 = Length of longer cable (1 m)

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Observations:
Observe the waveforms as shown below.

Input to Emitter Circuit (CH1-0.2V/div; TB- 0.5mS)

Detector output (for 0.5m Cable) Detector output (for 1m Cable)

(CH1-0.1V/div; TB- 0.5mS) (CH1-0.1V/div; TB- 0.5mS)

Calculation:
Recorded values are as follows.
V1 = 0.6V; V2 = 0.54V; L1= 0.5m; L2= 1.0m
=> α = - [log (V1 / V2 )] / (L1 + L2)
= - (0.18/1.5) = (- 0.12) nepers / meter
= -(0.12) * 8.686 dB
= -1.0 dB approx.

Questions:
● How to measure propagation losses?
● By what optical cable is made up of?
● What is step index Fiber?

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Experiment 8
Objective: Study of Bending Loss
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
● Mandrel
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect Function Generator 1 KHz sine wave output to emitter input.
 Connect 0.5 m optic fiber between emitter output and detectors input.
 Connect Detector output to amplifier input.
Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Switch ‘On’ the Power Supply of the TechBook and Oscilloscope.
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Set the Oscilloscope channel 1 to 0.5 V/ Div and adjust 4-6 div amplitude by
using X 1 probe with the help of variable pot in Function Generator Block at
input of Emitter.
Observe the output signal from detector on Oscilloscope.
Adjust the amplitude of the received signal as that of transmitted one with the
help of gain adjusts potentiometer in AC amplifier block. Note this amplitude
and name it V 1 .
● Wind the fiber optic cable on the mandrel and observe the corresponding AC
amplifier output on Oscilloscope, it will be gradually reducing, showing loss
due to bends.
Observations:
Observe the waveforms as shown below.

Input to Emitter Circuit (CH1-0.2V/div; TB- 0.5mS)

Detector output (for 1m Cable) Detector output (after bending)

(CH1-0.1V/div; TB- 0.5mS) (CH1-0.1V/div; TB- 0.5mS)
Questions:
 What is the reason of bending losses?
 What is core and cladding?
 What is the function of cladding?

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Experiment 9
Objective: Measurement of Optical Power using optical power meter
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fiber cable
● Scientech Oscilloscope with necessary connecting probe
● Power Meter Scientech 2551 with Power Supply cord
Connection Diagram:

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Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Connect the fiber optic cable between emitter output & power meter.
Put the mode switch in emitter block to analog mode.
Connect the Scientech 2551 Optical Power Meter to emitter input.
Keep the power meter wavelength selector switch in 660 nm.
● Switch ‘On’ the Power Supply of the TechBook and Power meter.
● Note the reading displayed in power meter. It will be -13.4dB approximately.
● Switch the wavelength selector switch to 950 nm positions
● Observe the difference in the reading due to wavelength mismatching shows the
importance of the wavelength selection in measurement of light.
Questions:
● How the power is measured using power meter?
● What is wavelength of light?
● What do you understand by fiber bending?

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Experiment 10
Objective: Measurement of Propagation Loss in optical fiber using optical power
meter
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
● Scientech 2551 – Optical Power Meter
Connection Diagram:

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Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Keep the mode switch in emitter circuit in analog mode.
Connect the 0.5m fiber cable in between the emitter LED & input of power
meter.
 Connect the Scientech 2551 Optical Power Meter to emitter input.
 Keep the power meter wavelength selector switch in 660 nm.
 Switch ‘On’ the Power Supply of the TechBook and Power meter.
Note the reading in power meter.
Replace the 0.5m fiber cable with the 1m cable without disturbing any setting.
Again note the reading in power. This reading will be lesser then the previous
one, indicating that the propagation loss increases with increase in length.

Observation and Calculation:

Power meter reading for 0.5 m cable = -13.4dB approximately.
Power meter reading for 1 m cable = -14.0dB approximately.
Propagation Loss = 0.6dB

Questions:
● How Propagation Loss in optical fiber is measured?
● What are the various types of losses in fiber?
● What is the formula used for measurement of losses?

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Experiment 11
Objective: Measurement of Numerical Aperture (NA) of optical fiber
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
● Numerical Aperture measurement Jig
Connection Diagram:

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Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Put the mode switch SW1 to Digital to drive the emitter in digital mode.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Connect the Frequency Generator 1 KHz sine wave output to input of emitter
circuit. Adjust its amplitude at 5Vp-p.
Connect one end of fiber cable to the output socket of emitter circuit and the
other end to the numerical aperture measurement jig. Hold the white screen
facing the fiber such that its cut face is perpendicular to the axis of the fiber.
Hold the white screen with 4 concentric circles (10, 15, 20 & 25 mm diameter)
vertically at a suitable distance to make the red spot from the fiber coincide with
10 mm circle.

Record the distances of screen from the fiber end L and note the diameter W of
the spot.
Compute the numerical aperture from the formula given below.
W
N.A. =
4L W2
2

= Sin max (acceptance angle)

Vary the distance between in screen and fiber optic cable and make it coincide
with one of the concentric circles. Note its distance.
Tabulate the various distances and diameter of the circles made on the white
screen and computer the numerical aperture from the formula given above.

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Observation and Calculation:

Sr. Diameter ‘W’ Distance ‘L’ NA= W / √( 4L2 + W2)

1 10 13 0.35

2 15 20 0.35

3 20 27 0.35

4 25 34 0.35

Inferences:
The numerical aperture as recorded in the manufacturer's data sheet is 0.5 typically.
The value measured here is 0.35. The lower reading recorded is mainly due to the
fiber being under filled.

Questions:
● What is numerical aperture?
● Write the formula for numerical aperture?
● What is the significance of numerical aperture?

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Experiment 12
Objective: Study of Characteristics of E-O converter using optical power meter
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
● Scientech 2551 – Optical Power Meter
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Put the mode switch in emitter block to digital mode.
Connect the variable supply output to the emitter input.
Adjust the supply potentiometer to its minimum setting fully counter clockwise.

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Connect the fiber optic cable between the emitter LED and Optical Power meter.
Switch ‘On’ the Power Supply of TechBook and power meter.
Note the reading in power meter.
Vary the supply potentiometer so as to vary the voltage applied to emitter LED.
Record the change in power meter reading corresponding to change in forward
voltage.
● Plot the graph between forward voltage and power meter reading.
Observation:
Sr. Vin (DC) Po (Approx.)
1 1.0V -61.0dB
2 1.3V -60.0dB
3 1.4V -59.0dB
4 1.5V -50.0dB
5 1.6V -40.0dB
6 1.7V -30.0dB
7 1.8V -25.0dB
8 1.9V -20.0dB
9 2.0V -15.0dB
10 2.1V -12.0dB
11 2.2V -10.0dB
12 2.3V -09.8dB
13 2.4V 09.8dB
14 2.5 09.8dB

Questions:

● What is the function of optical power meter?

● What is the full form of LED?
● Why LED is not used for long distance transmission?

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Experiment 13
Objective: Study of Characteristics of Fiber Optic Communication Link
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
Connection Diagram:

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Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the following connections as shown in next figure
 Connect Function Generator 1KHz sine wave output to emitter input.
 Connect optic fiber between emitter output and detector input.
 Connect detector output to amplifier input.
Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.

Set the amplitude of the Function Generator to 2 Vp-p.

Observe the transmitted and received signal on Oscilloscope. Vo (output
voltage) should be in the same order as Vin (input voltage).
Next set Vin to suitable values and note the values of Vo.
● Tabulate and plot a graph Vo versus Vin & compute Vo/ Vin.
Observation:
Sr. Vin pp Vo pp (Approx.)
1 1.0V 2.0V
2 2.0V 4.0V
3 3.0V 6.0V
4 4.0V 8.0V
5 5.0V 10.0V

Questions:
● What are the characteristics of fiber optics link?
● What is the function of transmitter?
● How light signals are converted back to the electrical signals?

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Experiment 14
Objective: Study of Voice Communication through fiber Optic cable using
Amplitude Modulation.
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
● Scientech Oscilloscope
Connection Diagram:

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Scientech 2501A Optical Fiber Communication

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the following connections as shown in next figure
 Connect the audio input block input to microphone.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to input of amplifier.
 Connect the output of audio input block to emitter input.
 Connect the AC amplifier output to input of audio output block.
Put the mode switch SW1 to Digital to drive the emitter in digital mode.
Turn the 1 KHz potentiometer in Function Generator block to fully clockwise
(maximum amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
With the help of dual trace Oscilloscope observe the input signal at emitter
input. Also, observe the output from the detector. It should carry a smaller
version of the original 1 KHz sine wave, illustrating that the modulated light
beam has been reconverted into an electrical signal.
The output from detector is further amplified by AC amplifier this amplifier
increases the amplitude of the received signal, and also removes the DC
component, which is present at detector output. Monitor the output of Amplifier
and adjust the gain adjust potentiometer until the monitored signal has same
amplitude as that applied to emitter input.
While monitoring the output of Amplifier change the amplitude of modulating
sine wave by varying the 1 KHz potentiometer in the Function Generator block.
Note that as expected, the amplitude of the receiver output signal changes.
Observe that same audio output is available on the speaker as fed to the
microphone.
Questions:
● What is the advantage of amplitude modulation in terms of bandwidth
requirement?
● How amplitude modulation signal is generated?
● What is the detection process amplitude modulated signals?

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Experiment 15
Objective: Demonstration of Voice Transmission through optical fiber using FM
Equipments Required:
● Scientech 2501A TechBook with Power Supply and mains cord
● Optical Fibre cable
● Scientech Oscilloscope
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Make the following connections as shown in next figure
 Connect the frequency modulator output to the emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Detector output to comparator input.
 Comparator output to the PLL detector input.
 PLL detector output to the low pass filter input.
 Low Pass Filter output to AC amplifier input.
 Plug the microphone in the input of audio input block.

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 Output of audio input block to input of FM block.

 Output of AC amplifier block to input of audio output block.
Put the mode switch SW1 to Digital to drive the emitter in digital mode. This
ensures that fast changing digital signal applied to the driver input causes the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in the Function Generator block to fully anti-
clockwise (zero amplitude) position.
Switch ‘On’ the Power Supply of the TechBook.
Monitor the output of the voltage controlled oscillator (VCO) in the frequency
modulator block. Note that the frequency of this digital signal is at present
constant, since the modulating 1 KHz Sine wave has zero amplitude.
Examine the output of the detector and check that the transmitted digital pulses
are successfully detected at the receiver.
With the help of dual trace Oscilloscope monitor both the inputs to the
comparator. Now adjust the bias potentiometer until the bias input is halfway
between the top and bottom of the square wave. You will remember that the
function of the comparator is to ‘clean up’ the square wave after its transmission
through the fiber optic link
The output of comparator drives the input of the PLL detector, which produces a
signal whose average level is proportional to the frequency of the digital stream.
This average level is then extracted by low pass filter and amplified by AC
amplifier to produce the original analog signal at the amplifiers output. Examine
and note that the output voltage is zero. This is expected since there is currently
no modulating voltage at the transmitter.
While monitoring the input to the frequency modulator block and the output
from AC Amplifier turn the 1 KHz potentiometer to its fully clockwise
maximum amplitude) position. Note that the modulating 1 KHz signal now
appears at the amplifiers output. If necessary, adjust the amplifiers gain adjust
potentiometer until the two monitored signal are equal in amplitude.
In order to fully understand how this frequency modulation transmitter/receiver
system works, examine the inputs and outputs of all functional blocks within the
system, using an Oscilloscope.
● Speak in the Microphone and listen the same in the speaker/headphone
Questions:
● What is the drawback of FM modulation in terms of bandwidth requirement?
● How the FM signals are generated?
● What is the function of AC amplifier?

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Experiment 16
Objective: Study of Voice Transmission through optical fiber using PWM
Equipments Required:
● Scientech 2501A TechBook with Power Supply and mains cord
● Optical Fibre cable
● Scientech Oscilloscope
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Make the following connections as shown in next figure
 Pulse width modulator output to emitters input.
 Connect the fiber optic cable between emitter output and detector input.
 Detector output to comparator & input.
 Comparator output to the LPF detector input.
 LPF output to AC amplifier input.

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 Plug the microphone into input of audio input block.

 Output of audio input block to input of PWM block.
 Output of AC amplifier block to input of audio output block.
Put the mode switch SW1 to Digital to drive the emitter in digital mode. This
ensures that fast changing digital signals applied to the driver input cause the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in Function Generator block to fully
anticlockwise (zero amplitude) position.
Switch ‘On’ the Power Supply of the TechBook and Oscilloscope.
Monitor the output of the pulse width modulator block. Note that the pulse
width of this digital signal is at present constant, since the modulating 1 KHz
sine wave has zero amplitude.
Examine the output of the detector and check that the transmitted digital pulses
are successfully detected at the receiver.
Monitor both input comparator and if necessary, slowly adjust the comparator
bias potentiometer, until the DC level on the negative input lies midway
between the high and low level of the signal on the positive input.
The average level of comparator output is extracted by LPF and then amplified
by AC amplifier, which also removes the DC off set. Since the average level of
the comparator output is proportional to the pulse width, the original analog
signal appears at the amplifiers output. Examine and note that the output voltage
is zero. This is expected since there is currently no modulating voltage at the
transmitter.
While monitoring the input to the pulse width modulator block and the output
from AC amplifier turn the 1 KHz potentiometer to its fully clockwise
(maximum amplitude position.). Note that the modulating 1 KHz signal now
appears at the amplifiers output. If necessary, adjust the amplifiers gain adjust
potentiometer until the two monitored signals are equal in amplitude.
In order to fully understand how this pulse width modulation transmitter/
receiver system works, examine the inputs and outputs of all functional blocks
within the system using an Oscilloscope.
● Observe that the same audio sound is available in the speaker as fed to
microphone.
Questions:
● What is frequency band for voice signals?
● By what means the voice signals are converted into electrical signals?
● Why PWM method is generally preferred for communication system?

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Experiment 17
Objective: Study of the effects of Switched Fault Number 1 & 8 on Amplitude
Modulation System
Equipments Required:
Scientech 2501A TechBook with Power Supply cord
Optical Fibre cable
● Scientech Oscilloscope
Connection diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the Function Generator output marked 1 KHz sine wave to input of
emitter.
 Connect the fiber optic cable between emitter output and detector input.

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Scientech 2501A Optical Fiber Communication

 Connect the detector output to input of the AC amplifier.

Put the mode switch SW1 to Analog to drive the emitter in analog mode.
Turn the 1 KHz potentiometer in Function Generator block to fully clockwise
(maximum amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
With the help of dual trace Oscilloscope observe the input signal at emitter.
Also, observe the output from the detector. It should carry a smaller version of
the original 1 KHz sine wave, illustrating that the modulated light beam has
been reconverted back into an electrical signal.
The output from detector is further amplified by AC amplifier this amplifier
increases the amplitude of the received signal and also removes the DC
component, which is present at detector output. Monitor the output of Amplifier
and adjust the gain adjust potentiometer until the monitored signal has the same
amplitude as that applied to emitter input.
Switch ‘On’ fault number 1. All other faults are set to ‘Off’.
This fault disconnects the input to emitter LED in analog mode so that distortion
occurs when analog amplitude modulation takes place.
Observe the output of AC amplifier block and also of each stage.
Switch ‘Off’ fault number 1 and check that A.M. system is operating correctly.
Adjust the potentiometer to provide a sinusoidal signal of 4 V peak to peak at
the output.
Switch ‘On’ fault number 8. This shorts the output and negative input of AC
amplifier; so that amplifier gain is always +1 irrespective of the position of the
gain adjust potentiometer.
Observe the output, and vary the gain adjust potentiometer. No change will be
observed in the output.
Switch ‘Off’ fault number 8.
● Switch ‘Off’ the Power Supply of the TechBook.
Questions:
● What is amplitude modulation?
● What is the advantage of using Amplitude modulation?
● What is depth of modulation?

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Experiment 18
Objective: Study of the effects of Switched Fault Number 4, 5 & 7 in FM System
Equipments Required:
● Scientech 2501A TechBook with Power Supply cord
● Optical Fibre cable
● Scientech Oscilloscope
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are ‘Off’.
Make the connections as shown in next figure
 Connect the Function Generator 1 KHz sine wave signal to frequency
modulator input.
 Connect the frequency modulator output to the emitter input.
 Connect the fiber optic cable between emitter output and detector input.

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 Detector output to comparator input.

 Comparator output to the PLL detector input.
 PLL detector output to the Low Pass Filter input.
 Low Pass Filter output to AC Amplifier input.
Put the mode switch SW1 to Digital to drive the emitter in digital mode. This
ensures that fast changing digital signal applied to the drivers input causes the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in Function Generator block to fully clockwise
(maximum amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Check that the FM System is operating correctly.
Switch ‘On’ fault number 4. All other faults are set to ‘Off’.
This fault affects the phase locked loop detector between the voltage controlled
oscillator (VCO) and phase comparator (exclusive OR gate). The result is that
the PLL no longer follows changes in the frequency of the input signal.
Observe the AC amplifier output and the output of PLL block.
Switch ‘Off’ fault number 4.
Switch ‘On’ fault number 7. This changes the DC bias on frequency Modulator
VCO input from + 2.5 V to 0V, so that the VCO no longer oscillates irrespective
of the signal applied to its input.
Observe the system output and the FM block output.
Switch ‘Off’ fault number 7.
Switch ‘On’ fault number 5 and observe the output of AC amplifier and also
PLL out put.
Switch ‘Off’ fault number 5 and check the operation of PLL System.
Questions:
● What is the function of VCO?
● What is FM?
● What is the function of PLL while detecting the transmitted signals?

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Experiment 19
Objective: Study of the effects of Switched Fault Number 2, 3 & 6 on Pulse Width
Modulation System
Equipments Required:
● Scientech 2501A TechBook with Power Supply and mains cord
● Optical Fibre cable
● Scientech Oscilloscope

Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are set to off.
Make the connections as shown in next figure
 Connect Function Generator 1 KHz sine wave signal to the Pulse Width
Modulator input.
 Pulse width modulator output to emitter input.

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 Connect the fiber optic cable between emitter output and detector input.
 Detector output to comparator input.
 Comparator output to the LPF detector input.
 LPF output to AC amplifier input.
Put the mode switch SW1 digital to drive the emitter in digital mode. This
ensures that fast changing digital signals applied to the driver input cause the
emitter LED to switch quickly between ‘On’ & ‘Off’ states.
Turn the 1 KHz potentiometer in Function Generator block to fully
anticlockwise (zero amplitude) position.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Check the correct operation of the PWM System.
Switch ‘On’ fault number 2. This open circuits the feed back loop of the first
stage of detector voltage amplifier, so that the final amplifier output saturates.
Observe the output at detector it saturates at +10V, and observe the system
output it should be zero. Try to the explain reasons behind it.
Switch ‘Off’ fault number 2.
Switch ‘On’ fault number 3.
This disconnects the input of comparator & hence the system output goes to
zero.
Switch ‘Off’ fault number 3.
Switch ‘On’ fault number 6. This switches OFF constant current source to PWM
so that output level of modulator is permanently high.
Observe the output of PWM; it becomes permanently high and output of system
becomes zero. Try to explain reasons behind it.
Switch ‘Off’ fault number 6 & check the correct operation of PWM System.
Questions:
● What is the significance of Switched Faults?
● What is full form of PWM?
● What is the function of PWM?

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Experiment 20
Objective: Determination of Bit Rate supported by the fiber optic link
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Scientech Function Generator 3 MHz
● Scientech Oscilloscope
Connection Diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the 1 KHz square wave from Function Generator to emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to comparator input.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode. This
ensures that signal applied to the driver input cause the emitter LED to switch
quickly between ‘On’ & ‘Off’ states.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.

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Examine the input to emitter on an Oscilloscope this 1 KHz square wave is now
being used to amplitude modulates emitter LED.
Examine the output of detector. This should carry a smaller version of original 1
KHz square wave illustrating that the modulated light beam has been
reconverted into an electrical signal.
Monitor inputs of comparator and slowly adjust the comparator bias
potentiometer until the DC level on the negative input lies mid-way between the
high & low level of the signal on the positive input. This DC level is
comparator's threshold level.
Examine the output of comparator. Note that the original digital modulating
signal has been reconstructed at the receiver.
Remove the on board TTL output from the emitter input and connect the TTL
output of square wave generator to emitter input.
Keep the frequency at 10 KHz. Observe the received output on the Oscilloscope.
Vary the frequency of the TTL input observing the output each time. The
comparator bias potentiometer can be adjusted, if required.
● Note the frequency at which the output is distorted or has become zero. The bit
rate supported by the link is twice the frequency reading corresponding to zero/
distorted output in bits per second.

Observation:
Observe the waveforms as shown below.

Input and output in dual mode (10 KHz) Input and Output in dual mode (480 KHz)
(CH1-2V/div; TB- 50uS) (CH1-2V/div; TB- 1uS)

Questions:
● How to determine the bit rate?
● What is optical Fiber link?

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Experiment 21
Objective: Determination of Sensitivity of the fiber optic link
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
Scientech Function Generator
Scientech 2551 – Optical Power Meter
Connection diagram:

Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Make the connections as shown in next figure
 Connect the 1 KHz square wave from Function Generator to emitter input.
 Connect the 0.5m fiber cable between emitter output and detector input.
 Connect the detector output to comparator input.

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Put the mode switch SW1 to Digital to drive the emitter in Digital mode. This
ensures that signal applied to the driver input cause the emitter LED to switch
quickly between ‘On’ & ‘Off’ states.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Examine the input to emitter on an Oscilloscope this 1 KHz square wave is now
being used to amplitude modulates emitter LED.
Examine the output of detector. This should carry a smaller version of original 1
KHz square wave illustrating that the modulated light beam has been
reconverted into an electrical signal.
Monitor inputs of comparator and slowly adjust the comparator bias
potentiometer until the DC level on the negative input lies mid-way between the
high & low level of the signal on the positive input. This DC level is
comparator's threshold level.
Examine the output of comparator. Note that the original digital modulating
signal has been reconstructed at the receiver.
Remove the on board TTL output from the emitter input and connect the output
of square wave from generator to the emitter input.
Observe the output of the detector on the Oscilloscope.
Remove the end of the fiber connected to the detector and connect it to the
Scientech 2551 optical power meter.
Note the reading on the power meter Po. This reading is the power being
transmitted to the receiver from the source.
Remove the fiber end which is connected to the power meter and connect it
again to the receiver.
Slowly reduce the amplitude of the square wave till the output being viewed on
the Oscilloscope reduces to zero.
● Remove the fiber end from the receiver and connect it to the power meter. Note
the reading on the power meter Ps. This gives the measure of sensitivity of the
receiver.
Observation:
Po (at 1 KHz 5Vpp input) = -14dB approximately.
Ps (at 1 KHz 2Vpp input) = -35dB approximately.
Questions:
● Define the sensitivity?
● What are the elements of Fiber optics link?

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Experiment 22
Objective: Determination of Power Margin (Power Budget)
The Power margin is defined by:
PM = Po – Ps – Pi
Where,
Po is the power transmitted
Pi is the power lost in the fiber
Ps the sensitivity of the receiver
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
Scientech 2551 – Optical Power Meter
Connection diagram

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Procedure:
● From Experiment 21, assuming that the power lost in the 0.5m fiber Pi is
negligible, PO – Ps gives Power Budget of the link.
● Repeat Experiment 21 with 1 m fiber optic cable and find the Power Output P’O.
● Now calculate the Power Loss in cable = Pi = PO - P’O.
● Now calculate the Power Margin PM = Po –Pi – Ps.
Observation:
For 0.5m Fiber cable = PO – Ps = -13.4 dB – (-35 dB) = 21.6 dB
For 1m Fiber cable = P’O = -14.0 dB
Power Loss in cable = Pi = PO - P’O. = -13.4 - (-14.0) = 0.6 dB
Power Margin PM = Po –Pi – Ps. = 21.6 – 0.6 = 21dB
Questions:
● How to determine power Margin?
● What do you understand by power budget?

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Experiment 23
Objective: V-I characteristics of Photo LED
The aim of this experiment is to plot the V - I characteristic of LED.
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
Scientech Digital Multimeter
Theory:
LED’s and LASER diodes are the commonly used sources in optical communication
systems, whether the system transmits digital or analog signal. It is therefore, often
necessary to use linear electrical to optical converter to allow its use in intensity
modulation & high quality analog transmission systems. LED's have a linear optical
output with relation to the forward current over a certain region of operation.
Connection Diagram:

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Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are in OFF condition.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode.
Make connections as shown in the above figure
 Connect the variable Power Supply 1 to the emitter input. Keep the level
of the supply to minimum position.
 Connect an Ammeter between point ‘a’ and ‘b’ to measure the forward
current (If).
 Connect a Voltmeter between emitter input and variable Power Supply 2
to measure the forward voltage (Vf). Keep the level of the supply to
maximum position. It measures the voltage drop across the 1kohms
(connected in series with Photo LED) current limiting resistors.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Adjust the Power Supply potentiometer to its minimum setting fully counter
clockwise. Now look down the emitter LED socket and slowly advance the
setting of the potentiometer until in subdued lighting the light from LED is just
visible.
Vary the potentiometer gradually so as to vary the forward voltage (as 1.5,
2.0…..), note the corresponding If (forward current).
● Record these values of (Vf) and (If) & plot the characteristic between these two.
Observation:
Sr. Vf If (Approx.)
1 0.5V 0.5mA
2 1.0V 1 mA
3 1.4V 1.4 mA
4 1.5V 1.5 mA
5 1.6V 1.6 mA
6 v
1.7V 1.7 mA
7 1.85V 1.85 mA
8 2.15V 2.15 mA
9 2.75V 2.75 mA
10 3.25V 3.25 mA
11 3.9V 3.9 mA
12 4.0V 4 mA
13 4.0V 4 mA
14 4.0V 4 mA
15 4.0V 4 mA
16 4.0V 4 mA

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Experiment 24
Objective: V-I characteristics of Photo Detector
The aim of this experiment is to plot the V-I characteristic of Photo Detector.
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fibre cable
Scientech Oscilloscope
Scientech Digital Multimeter
Theory:
Photo Transistors and Photo Diodes are the commonly used detectors in optical
communication systems, whether the system receives digital or analog signal. It is
therefore, often necessary to use linear optical to electrical converter to allow its use
in intensity demodulation & high quality analog receiving systems. Photo Diodes
have a linear electrical output with relation to the light intensity over a certain region
of operation.
Connection Diagram:

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Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are in OFF condition.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode.
Make connections as shown in next figure
 Connect the variable Power Supply 1 to the emitter input. Keep the level of
the supply to minimum position.
 Connect a patch cord between point ‘a’ and ‘b’.
 Connect the fiber optic cable between emitter output and detectors input.
 Connect a Voltmeter between emitter input and variable Power Supply 2 to
measure the forward voltage (Vf). Keep the level of the supply to maximum
position. It measures the voltage drop across the 1kohms (connected in
series with Photo LED) current limiting resistors.
 Connect an Ammeter between point ‘c’ and ‘d’ to measure the detector
current (Id).
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Adjust the Power Supply potentiometer to its minimum setting fully counter
clockwise. Now look down the emitter LED socket and slowly advance the
setting of the potentiometer until in subdued lighting the light from LED is just
visible.
Vary the potentiometer gradually so as to vary the forward voltage and note the
corresponding detector current (Id).
● Record these values of (Vf) and (Id) & plot the characteristic between these two.
Observation:
Sr. Vf Id (Approx.)
1 0.5V 13uA
2 1.5V 26uA
3 1.6V 66uA
4 1.7V 200uA
5 1.85V 666uA
6 v
2.15V 1.7mA
7 2.75V 3.5mA
8 3.25V 6mA
9 3.9V 9.3mA
10 4.0V 9.5mA
11 4.0V 9.6mA
12 4.0V 9.66mA
13 4.0V 9.7mA
14 4.0V 9.7mA
15 4.0V 9.7mA

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Experiment 25
Objective: To Measure Bit Error Rate.
Apparatus Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fiber Cable
Scientech Oscilloscope
Theory:
In telecommunication transmission, the bit error rate (BER) is a Ratio of bits that have
errors relative to the total number of bits received in a transmission. The BER is an
indication of how often a packet or other data unit has to be retransmitted because of
an error. Too high a BER may indicate that a slower data rate would actually improve
overall transmission time for a given amount of transmitted data since the BER might
be reduced, lowering the number of packets that had to be resent.
Connection Diagram:

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Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are off.
Make the connections as shown in next figure
 Connect patch cords between ‘a & b’ and ‘c & d’.
 Connect the 64 KHz Clock from Clock generator to the Clock in socket of
PRBS Data generator.
 Connect PRBS Data Generator output to the emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to ‘Signal In’ socket of Noise Generator.
Put the selection switch towards Bit Error Counter Block to count the bit error.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode. This
ensures that signal applied to the driver input cause the emitter LED to switch
quickly between ‘On’ & ‘Off’ states.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Initially Adjust Level pot of Noise Generator at middle position.
Press the Start/Stop switch and observe the Error Count on 7-Segment Display
of Bit Error Counter for any time duration ‘Td’ and press the Start/Stop switch
again to stop.
Record the readings for different clock frequencies/Time duration/Noise level n
the following observation table.
Adjust Level pot for minimum and maximum position to observe effect of
variable noise on the error count.

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Calculation and Observations:

Sr. CLK Time Duration Total No. of Bit Error Bit Error
No. Frequency (Td) Transmitted Bits Count Rate
N = CLK * Td (E) = E/N

64000 * 5 =
1 64 KHz 5 Sec 1704 0.005325
320000

Measuring Bit Error Rate

A BERT (bit error rate tester) is a procedure or device that measures the BER for a
given transmission. The BER, or quality of the digital link, is calculated from the
number of bits received with error divided by the number of bits transmitted.
BER= Bits received with Error /Total bits transmitted
Observations:
 We can observe that for a fixed clock frequency, as we increase the level of
Noise, Bit Error Count increases.
 We can also observe that for a fixed level of Noise, Bit Error Count are less in
No. for lower clock frequencies and more for higher clock frequencies.

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Experiment 26
Objective: Study and Observation of Eye Pattern.
Apparatus Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fiber Cable
Scientech Oscilloscope
Theory:
The eye-pattern technique is a simple but powerful measurement method for assessing
the data-handling ability of a digital transmission system. This method has been used
extensively for evaluating the performance of wire systems and can also be applied to
optical fiber data links. The eye-pattern measurements are made in the time domain
and allow the effects of waveform distortion to be shown immediately on an
Oscilloscope.
Connection Diagram:

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Procedure:
Connect the TechBook Power Supply with mains cord to TechBook Scientech
2501A.
Ensure that all switched faults are off.
Make the connections as shown in next figure
 Connect patch cords between ‘a & b’ and ‘c & d’.
 Connect the 64 KHz Clock from Clock generator to the Clock in socket of
PRBS Data generator.
 Connect PRBS Data Generator output to the emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Connect the detector output to ‘Signal In’ socket of Noise Generator.
Put the selection switch towards Eye Pattern socket.
Put the mode switch SW1 to Digital to drive the emitter in Digital mode. This
ensures that signal applied to the driver input cause the emitter LED to switch
quickly between ‘On’ & ‘Off’ states.
Switch ‘On’ the Power Supply of TechBook and Oscilloscope.
Initially Adjust Level pot of Noise Generator at middle position.
Connect channel 1 (CH Y) of Oscilloscope to Eye Pattern Socket.
Connect EXT. TRIG. Of Oscilloscope to CLK In of PRBS Data Generator and
put the Oscilloscope in EXT. TRIG. mode.
Adjust the time base as well as ‘Cal potentiometer’ of Oscilloscope to get Eye
Pattern as shown in next figure.
Observe the Eye pattern for different clock frequencies and different Noise
Level.
Also observe the received data with no error, less error, and more error as shown
in figure.

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Observation:

Oscilloscope Setting

Eye Pattern: Without error & with error in data

Eye Pattern: Without error & with error in data

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Eye Pattern: Without error & with error in data

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Received Data with no error, less error and more error

Conclusion:
As clock frequency increases the EYE opening becomes smaller.

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Experiment 27
Objective: Determination of effect of Electromagnetic Interference over a Copper
track and a Fiber Optic cable.
Equipments Required:
Scientech 2501A TechBook with Power Supply and mains cord
Optical Fiber Cable
Scientech Oscilloscope
Theory:
Electromagnetic Interference:
Electromagnetic interference is a phenomenon of unwanted electromagnetic signals,
which may degrade the performance of an electronic device. Electromagnetic
interference is defined to exists when undesirable voltage or currents are present to
influence adversely the performance of an electronic circuit or system. Interference
can be within system (intera-system), or it can be between systems (inter system). The
system is the equipment or circuit over which one exercises design or magnetic
control.
What are the causes of EMI?
Uncontrolled conductive path and radiated near/ far fields cause EMI. The cause of an
EMI problem is an unplanned coupling between a source and a receptor by means of
transmission path.
What are the effects of EMI?
The Electromagnetic interference degrades the performance of electronic systems.
EMI can be attributed to either intentionally or unintentionally generated
electromagnetic energy. The purposeful generated electromagnetic energy for
communication defined as intentionally generated EMI which has allowable limits as
well as measurement techniques on Radio Frequency noise / interference has been set
at national and international level.
Control:
The control of Electromagnetic Interference is best achieved by good interference
control principles during the design process. These involve selection of signal levels,
impedance levels, frequencies and circuit configuration that minimize conducted and
radiated interference. In addition, signal levels should be selected to be as low as
possible, while being consistent with the required signal to noise ratio. Impedance
levels should be chosen to minimize undesirable capacitive and inductive coupling.
Physically separated leads carrying current from different sources also achieve
interference control.
For optimum control three major methods of EMI suppression, grounding, shielding
and filtering should be incorporated in the design process.

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Grounding is the process of electrically establishing a low impedance path between

two or more points in a system. An ideal ground plane is zero potential, zero
impedance body that can be used for a reference for all signals in the system.
Shielding is the process of confirming radiated energy to the bounds of specific
volume or preventing radiated energy from reaching a specific volume. Coaxial cables
are one of the mediums used for such application.
Connection Diagram:

Procedure:
● Connect the power supply cord to the main power plug & to Techbook
Scientech 2501.
● Ensure that all switched faults are OFF.
● Make the connections as shown in figure above.
 Connect the function generator 1 KHz sine wave output to input of a copper
track.
 Connect high frequency output of 4 .096 MHz to the input of the coil.
 Connect the other terminal of the coil to ground point.
● Set the output level of Function generator 1 KHz sine wave to 1V.
● Observe the output at the other end of the copper track on the oscilloscope.
● You will observe the distortion in the sine wave as high frequency signal is
superimposed on low frequency signal flowing through a nearby track.

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● Make the connections as shown in figure above.

 Connect the function generator 1 KHz sine wave output to emitter input.
 Connect the fiber optic cable between emitter output and detector input.
 Connect high frequency output of 4 .096 MHz to the input of the coil.
 Connect the other terminal of the coil to ground point.
 Place the fiber cable on the electrical link.
● Connect the detector output to oscilloscope.
● You will observe no distortion in detected sine wave as fiber optic cable is free
from Electromagnetic Interference.

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Frequently Asked Questions

● How Fiber optics is fabricated?
Fiber optics has been fabricated from materials that transmit light and are made
from a bundle of very thin glass or plastic Fibers enclosed in a tube. One end is
at a source of light and the other end is a camera lens, used to channel light and
images around the bends and corners.
● What is Fiber optics?
Fiber optics has a highly transparent core of glass, or plastic encircled by a
covering called "cladding". Light is stimulated through a source on one end of
the Fiber optic and as the light travels through the tube, the cladding is there to
keep it all inside.
● Why single mode Fibers are used for long distance transmission?
The single-mode Fiber optic is used for high speed and long distance
transmissions because they have extremely tiny cores and they accept light only
along the axis of the Fibers. Tiny lasers send light directly into the Fiber optic
where there are low-loss connectors used to join the Fibers within the system
without substantially degrading the light signal.
● What is the drawback of multimode Fibers?
Multi-mode Fibers which have much larger cores and accept light from a variety
of angles and can use more types of light sources. Due to this reason they cannot
be used over long distances transmissions.
● What is optical Fiber?
The Fiber optic cable consists of two concentric layers of transparent materials.
The inner portion the core transports the light, the outer covering the cladding
must have a lower refractive index than the core so the two of them are made up
of different materials.
● List the advantages of optical Fiber as waveguide?
Advantages of FIBER Optic System are as follows:
Enormous Potential Band Width (BW)
Small size and weight
Electrical Isolation
Immunity to Interference and Cross talk
Signal Security
Low transmission loss
Potential Low Cost
Thinner
Non-flammable
Ruggedness and flexibility
Low cost and availability
Reliability

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● List the disadvantages of optical Fibers as waveguide?

Disadvantages of optical fibers systems are as follows:
Price
Fragility
Affected by chemicals
Opaqueness
Requires special skills
● What is meant by index profile?
Index profile is the refractive index distribution across the core and the cladding
of a fiber.
● What is step index profile?
Step index profile in which core has one uniformly distributed index and the
cladding has a lower uniformly distributed index.
● What is graded index profile?
Graded index profile, in which refractive index varies gradually as a function of
radial distance from the fiber centre.
● What is the principle of operation of Optical Fiber?
The principle of operation of optical Fiber lies in the behaviour of light. It is a
widely held view that light always travels in straight line and at constant speed.
Of course, the light propagates in straight lines, but when it is reflected inside
the optical Fiber million and trillion times by the clad, each movement
comprising of a straight line and consequently because of such reflections, it
acquires the shape of the optical Fiber. So effectively, it is said to have been
travelling along the Fiber. It changes its direction only if there is a change in the
dielectric medium.
● How refractive index is defined?
Refractive index of a medium is defined as the ratio of velocity of light in
vacuum to velocity of light in medium.
Velocity of light in vaccum
Refractive index =
Velocity of light in medium

● How refraction occurs?

When a ray is incident on the interface between two dielectrics of differing
refractive indices, refraction occurs.
● What is partial internal reflection?
If the light is refracted and also partly reflected internally in the same medium
then it is referred as Partial Internal Reflection.

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● What Snell's law of refraction states?

The angle of incidence 1 and refraction 2 are related to each other and to
refractive indices of dielectrics by Snell's law of refraction which states that:
n
1sin1 n
2sin2
sin 1 n2
sin 2 n1
It is this change in refractive indices which causes the change in the path of the
incident ray as evident from the Snell’s law. Larger the change in the refractive
indices larger change in the direction of the incident ray.
● What is the relationship between incident ray and angle of refraction?
As the angle of incident ray increases, the angle of refraction also increases even
faster and when the angle of refraction becomes 90° thereafter, if the angle of
incidence is increased a condition is arrived where the incident ray is totally
reflected in the same medium from where it has emerged; this is referred as the
total internal reflection.
● How the critical angle is defined?
Since, the angle of refraction is always greater than the angle of incidence, when
the incident medium is denser than the refraction medium. Thus, the angle of
refraction is 90° and the refracted ray emerges parallel to the interface between
the dielectrics. This is the limiting case of refraction and this angle of incidence
is known as critical angle c .
● What is total internal reflection?
At angles of incidence greater than the critical angle the light is reflected back
into the originating dielectric medium. This behaviour of light is termed as Total
Internal Reflection.
● What is the condition of total internal reflection?
Angle of Incidence = Angle of Reflection
● What is acceptance angle?
The maximum angle to the axis at which light may enter the fiber in order to be
propagated hence it is referred to as the acceptance angle for the fiber.
● What is numerical aperture?
It gives the relationship between the acceptance angle and the refractive indices
of the three media involved viz. the core, the cladding and air.

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● Write the formula for numerical aperture?

22 1
/
2 22
N
u
m
er
i
c
al
Ap
er
t
ur
ens
i
0na(
n1n)
2 (
n
1 n
)
2

(
n
1n)
(
2n
1n
2)
Where,
n0 = Refractive index of air
n1 = Refractive index of core
n2 = Refractive index of cladding
● What is the significance of Numerical Aperture?
The Numerical Aperture is a very useful measure of light collecting ability of a
fiber. It directly relates to the refractive indices of the core and cladding. As we
observe from the above equation, greater the absolute value of the indices of
core and cladding, greater the numerical aperture; similarly, greater the
difference between the refractive indices greater the numerical aperture.
● Give the classification of optical fiber?

● What is single mode fiber?

In single mode fiber only one mode (Electromagnetic wave) is able to
propagate.
● Where the single mode fiber is used?
This is used in long distance and/or, high-speed communication.
● Why single mode fiber is used for long distance transmission?
It is beneficial over long distances since it completely eliminates a problem
known as Intermodal Dispersion associated with Multimode cables.
● What is the dimension of core and cladding for single mode?
Core: 8.3 um
Cladding: 125 um

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Scientech 2501A Optical Fiber Communication

● What is the meaning of multi mode fiber?

The term multimode means that the diameter of the fiber optic core is large
enough to propagate more than one mode (Electro Magnetic Wave).
● What is dispersion?
Because of the multiple modes the pulse that is transmitted down the fiber tends
to become stretched over distance this is referred to as dispersion.
● What is the effect of dispersion?
Available bandwidth is reduced.
● What is the application of multimode fiber?
These are typically used in applications such as LAN (Local Area Networks) &
FDDI (Fiber Distributed Area Interface)
● What is the dimension of core and cladding for multi mode?
Core: 50 um
Cladding: 125 um
● What are the various losses in optical fiber?
Losses in Optic Fiber are as follows:
● Attenuation
● Material Absorption Losses
● Linear Scattering Losses
Ray Leigh Scatter
Mie Scattering
● Non Linear Scattering
● Micro Bending and Macro Bending
● Dispersion
Inter modal Dispersion
Intra modal Dispersion
● What are the reasons for attenuation of signals?
Several mechanisms are involved, including absorption by materials within the
fiber, scattering of light out of the core caused by environmental factors. The
degree of attenuation depends on the wavelength of light transmitted.
● What is the definition of attenuation?
Attenuation measures the reduction in signal strength by comparing output
power with input power. Measurements are made in decibels (dB). It is defined
as: -
Pi
DB loss = 10 log 10 P
o

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Scientech 2501A Optical Fiber Communication

● What material absorption loss indicates?

It is a loss mechanism related to the material composition and fabrication
process of the fiber that result in the dissipation of some of the transmitted
optical power as heat in wave-guide.
● What is linear scattering means?
Linear scattering mechanisms cause the transfer of some or all of the optical
power contained within one propagating mode to be transferred linearly
(proportionally) into a different mode.
● Why scattering of light occurs in optical fibers?
This process tends to result in attenuation of the transmitted light as the transfer
may be to a leaky or radiation mode that doesn't continue to propagate within
the fiber core, but is radiated from the fiber.
● Give the types of scattering?
Ray Leigh Scattering
Mie Scattering
● What is backscattering?
When the infrared light strikes a very-very small place where the materials in
the glass are imperfectly mixed, this gives rise to localized changes in the
refractive index resulting in the light being scattered in all directions. Some of
the light escapes the optic fiber, some continues in the correct direction and
some is returned towards the light source. This is called backscatter.
● What are the causes of Mie Scattering?
These result from the non - perfect cylindrical structure of the wave-guide. It
may be the caused by the imperfections such as irregularities in the core
cladding interface core, cladding refractive index difference along the fiber
length, diameter fluctuations, strains and bubbles. The scattering created by such
in homogeneities is mainly in the forward direction.
● What is micro bending?
A problem that often occurs in cabling of the optical fiber is the twisting of the
fiber core axis on a microscopic scale within the cable form. This phenomenon,
known as micro bending result from small lateral forces exerted on the fiber
during the cabling process and it causes losses due to radiation in both
multimode and single mode fiber.
● What happens when sharp bend occurs in fiber?
The light propagates down the optic fiber solely because the incident angle
exceeds the critical angle. If a sharp bend occurs, the normal and the critical
angle move round with the fiber. The incident ray continues in a straight line
and it finds itself approaching the core - cladding boundary at an angle less than
the critical angle and much of light is able to escape.

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● What is the effect of dispersion on light in optical fiber?

When an electrical pulse energizes a LASER, it launches a short flash or light
along the optic fiber. It is an unfortunate fact that the light burst becomes longer
as it moves along the fiber optic cable. The light spreads out.
● List the types of dispersion?
There are two types of Dispersion:
Inter modal Dispersion
Intra modal Dispersion
● What is the condition for light to be entered into the optical fiber?
Light to be propagated down the core of the optic fiber, the light must enter at an
angle greater than the critical angle.
● How the spreading of pulses occurs in Inter model dispersion?
When each and every ray is propagated at its own angle will arrive at slightly
different times at the far end. This spreading effect will occur all along the fiber
so it is also important to appreciate that the longer the optic fiber, the greater the
dispersion. Transmission rates that are actually possible on an optic fiber
therefore depend in its length.
● What is the effect of change in refractive index on light?
A change in refractive index will change the speed of that particular wavelength
of light.
● What is Intra modal Dispersion?
When the light source produces different wavelengths at the same time, the
components of the transmitted light pulse travelling at the same time, and then
the components of the transmitted light pulse travelling at different speeds. The
total package of light will spread out - hence the Intra modal dispersion occurs.
● How to cure inter modal Dispersion?
A large core diameter means many modes and severe inter modal dispersion.
The cure for this type of dispersion is quite simple. Reduce the core size; the
number of modes decreases and inter modal dispersion is reduced.
● How inter modal Dispersion is completely eliminated?
To eliminate inter modal dispersion completely simply make the core so small
that only one mode is propagated. A single ray cannot possibly go at two
different speeds so inter modal dispersion cannot occur.
● Why LASER is used to reduce intra modal dispersion?
The LASER would cause less intra modal dispersion because its light is more
concentrated around the central wavelength.
● What is spectral width?
The spread of wavelength measured between the points where the power output
falls to half of the peak power is called the spectral width.

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Scientech 2501A Optical Fiber Communication

● Why LASER is used for long distance transmission?

Some LASERS have spectral widths as low as 0.1 nm (nanometre). The low
spectral width together with its high power and fast switching makes the
LASER first choice for long distance communications using single mode optic
fiber.
● What is full form of OTDR?
Optical Time Domain Reflectometer
● What is the function of OTDR?
The OTDR is a measuring instrument that uses backscatter. It is the most
versatile piece of test equipment that we have for making measurements on fiber
optic systems.
● What can be measured with the help of OTDR?
It provides us with two different measurements:
● It can measure the magnitude of any losses that occur along optic fiber.
● It can measure distance along the optic fiber.
● Where fiber optics links can be used?
Fiber optic links can be used for transmission of digital as well as analog
signals.
● Fiber optics links consists of how many elements?
Basically a fiber optic link contains three main elements, a transmitter, an
optical fiber and a receiver.
● What is the function of transmitter, optical fiber and receiver?
The transmitter module takes the input signal in electrical form and then
transforms it into optical (light) energy containing the same information. The
optical fiber is the medium, which takes the energy to the receiver. At the
receiver light is converted back into electrical form with the same pattern as
originally fed to the transmitter.
In this system the information signal is used to control the Intensity of the
source. At the far end, the variation in the amplitude of the received signal is
used to recover the original information signal.

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Scientech 2501A Optical Fiber Communication

Glossary of Fiber Optic Terms

● Acceptance Angle :
The angle over which, the core of an optical fiber accepts incoming light,
usually measured from the fiber axis.
● Angle of Incidence :
The Angle between incident ray and the normal to a reflecting or refracting
surface is called as Angle of Incidence.
● Attenuation :
Reduction of signal magnitude or loss normally measured in decibels. Fiber
attenuation is normally measured per unit length in decibels per kilo/meter.
● Avalanche Photodiode :
A semiconductor photo detector with integral detection and amplification stages
is called Avalanche Photodiode. Electrons generated at p-n junction are
accelerated in a region where they free an avalanche of other electrons. APD can
detect faint signals but require higher voltage than other semiconductor
electronics.
● Back Scattering :
Scattering of light in the direction opposite to that in which it was originally
travelling.
● Bandwidth :
The highest frequency that can be transmitted in analog operation is called as
bandwidth.
● Baud :
The number of signal level transitions per second in digital data for common
coding schemes, this equals bits per second.
● Bit Error Rate (BER) :
The fraction of bits transmitted incorrectly.
● Cladding :
The layers of glass or other transparent material surrounding the light-carrying
core of an optical fiber is called cladding. It has lower refractive index than the
core, and thus confines light in the core.
● Critical Angle :
The smallest angle at which a meridian ray may be totally reflected within a
fiber at the core - cladding interface is referred as critical angle.
● Core :
The central part of optical fiber that carries light is called core.
● Dark Current :
The noise current generated by a photo diode in dark is called Dark Current.

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Scientech 2501A Optical Fiber Communication

● Decibel :
A logarithmic comparison of power levels, defined as ten times the base ten
logarithm of the ratio of two power levels.
● Detector :
Transducer that provide an electrical output signal in response to an incident
optical signal. The current is dependent upon the amount of light received and
the type of device.
● Dispersion :
Distortion of an electromagnetic signal caused by different propagation
characteristics of different wave lengths and the differing path lengths of modes
in a fiber.
● Endoscopes :
A fiber - optic bundle used for imaging & viewing inside the human body.
● Fiber :
Any filament made of dielectric; a material that guides light, whether or not it is
used to transmit signal.
● Graded Index :
A fiber in which the refractive index changes gradually with distance from the
fiber axis, rather than abruptly at the core cladding interface is called Graded
Index.
● Index of refraction :
The ratio of velocity of light in a vacuum to the speed of light in a given
medium is called Index of refraction.
● Index Matching Gel :
A gel or fluid whose refractive index is close to the core index that reduces
refractive index discontinuities that can cause reflective losses is called as Index
Matching Gel.
● Intensity :
Power per unit solid angle is referred as intensity.
● Infrared :
Wavelength longer than 700 nm and shorter than about 1 nm is called Infrared.
We cannot see infrared radiation but can feel it as heat. Transmission in optical
fiber is best in infrared at wavelengths of 1100 -1600 nm.
● ISDN :
Aacronym of Integrated Services Digital Network is a digital standard calling
for 144 K bits/ second Transmission, corresponding to two 64 K bits/ sec. digital
voice channels and one 16 K bits / data channel.

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Scientech 2501A Optical Fiber Communication

● Laser :
Acronym of Light Amplification by Stimulated Emission of Radiation- A device
that produces monochromatic coherent light through stimulated emission most
LASERS used in fiber optic communication is a solid state semiconductor
device.
● LED :
Light Emitting Diode which is a semiconductor device that emits light from a p-
n junction. Light may exit from the junction strip edge or from its surface
(depending on device structure).
● Light :
Strictly speaking, electromagnetic radiation with properties similar to visible
light includes the invisible near - infrared radiation in most fiber optic
communication system.
● Mode :
An electromagnetic field distribution that satisfies theoretical requirement for
propagation in wave-guide is called modes.
● Micro bending :
Tiny bends in a fiber that allows light to leak out and increase loss.
● Macro bending :
In an optical fiber all macroscopic deviations of the axis from a straight line;
distinguished from micro bending.
● Meridian Ray :
A light ray that passes through the axis of optical fiber is called Meridian Ray. It
is generally used when illustrating the fundamental transmission properties of
optical fiber.
● Material Dispersion :
Light impulse broadening caused by various wavelengths of light travelling at
different velocities through a fiber is called Material dispersion. Material
dispersion increases with increasing spectral width of the source.
● Numerical Aperture (N A) :
A characteristic parameter of any given fiber light gathering capability defined
by the sine of half angle over which a fiber can accept light. It is multiplied by
the refractive index of the medium containing the light.
Numerical Aperture = n0 sin a = (n12 – n22) ½

● Noise Equivalent Power :

The r.m.s.(root mean square) value of optical power, which is required to
produce an r.m.s. signal to noise ratio of 1, and indication of noise level, which
defines the minimum detectable signal level.

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Scientech 2501A Optical Fiber Communication

● Optic fiber :
This is the length of clear material along which we propagate the light.
● Optical Time Domain Reflectometer (OTDR) :
A method for measuring transmission characteristics by sending a short pulse of
light through fiber and the resulting back scatter and reflection are measured as a
function of time. Useful in estimating attenuation coefficient as a function of
distance and identifying defects and other localized losses
● Polarization :
Alignment of the electric and magnetic fields that make up an electro magnetic
wave normally refers to the electric field. If all light waves have the same
alignment; light is said to be polarized.
● Raleigh Scattering :
Scattering by refractive index fluctuations (non-homogeneities in material
density or composition) that are small with respect to wavelength
● Reflectance :
The ratio of reflected power to incident power is called reflectance. In optics,
frequently expressed as optical density or as a percent in communication
applications, generally expressed in dB
● Radiometer :
An instrument distinct from photometer, to measure power (watts) of
electromagnetic radiation
● Responsively :
The ratio of detector output to input, usually measured in units of amperes per
watt.
● SMA :
Sub-miniature assembly
● Signal to Noise Ratio :
The ratio of signal to noise, measured in decibels, an indication of signal quality
in analog system.
● Skew Ray :
A ray that does not intersect the axis of a fiber is known as skew ray.
● Total Internal Reflection :
The total internal reflection occurs when light strikes an interface at angles of
incidence (with respect to normal) greater than the critical angle.
● Wavelength :
The distance an electromagnetic wave travels in the time it takes to oscillate
through a complete cycle. Wavelength of light is measured in nanometres or
micrometers.

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Scientech 2501A Optical Fiber Communication

Warranty
● We guarantee this product against all manufacturing defects for 12 months from
the date of sale by us or through our dealers.
● The guarantee will become void, if
• The product is not operated as per the instruction given in the Learning
Material.
• The agreed payment terms and other conditions of sale are not followed.
• The customer resells the instrument to another party.
• Any attempt is made to service and modify the instrument.
● The non-working of the product is to be communicated to us immediately giving
full details of the complaints and defects noticed specifically mentioning the
type, serial number of the product and date of purchase etc.
● The repair work will be carried out, provided the product is dispatched securely
packed and insured. The transportation charges shall be borne by the customer.
Hope you enjoyed the Scientech Experience.

List of Accessories
Quantity
 Patch Cord 16” (2mm) ................................................................................... 10
 Mains Cord.......................................................................................................1
 Power Supply ...................................................................................................1
 Head Phone .....................................................................................................1
 Microphone ......................................................................................................1
 Numerical Aperture (N.A.) Plate .....................................................................1
 Numerical Aperture Stand ...............................................................................1
 Mandrel ............................................................................................................1
 Fiber Optic Cable, Length 1 meter ..................................................................1
 Fiber Optic Cable, Length ½ meters. ...............................................................1
 Plastic Box for Cable .......................................................................................1
 Product Tutorial (CD) ......................................................................................1

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