LPU-Cavite

FAITH COLLEGES Fiber Optics

FIBER OPTICS is the science or technology of light Planck’s Law
transmission through very fine, flexible glass or plastic fibers. When visible light or high frequency electromagnetic radiation
illuminates a metallic surface, electrons are emitted.
OPTICAL FIBER is a glass or plastic fiber that carries light
along its length. Photon Energy
When making the transition from one
HISTORY E p  hf energy level to another, the atom
Alexander Grahambell absorbs or emits a packet of energy
 In 1880 he experimented the transmission of sound waves hc called a PHOTON.
over a beam of light using a device called Ep 
PHOTOPHONE. 
Heel,Hopkins, and Kapany
 In 1950’s they experimented with light transmission Reflection
through bundles of fibers. Phenomenon of wave motion, in which a wave returned after
 Led to the development of the FLEXIBLE FIBERSCOPE. impinging on a surface.

N.S. Kapany Refraction

 Coined the term “Fiber Optic” in 1956. The bending of light ray as it travels from one material to
another material with different density.
Theodore Maiman
 Built the first optical maser in late 50’s.

Kao & Bockham

 Proposed a new communications medium using cladded
fiber cables.

Fiber Optics Communications System

An electronic communication system that uses light as a carrier
of information.

Diffraction
The bending or spreading out of waves as they pass around
the edge or through a narrow aperture.

Dispersion
The separation of visible light or other electromagnetic waves
into different wavelengths.

Critical Angle
Advantages The minimum angle of incidence at
 Greater information capacity n  which light ray may strike the interface
 Immunity to crosstalk C  sin1  2  of two media and result in an angle of
 Immunity to static interference  n1  refraction of 90°.
 Environmental immunity
 Safety Index of Refraction
 Security The refractive index of a substance measures how the
 Durability and reliability substance affects light travelling through it. It is equal to the
 Economics speed of light in a vacuum divided by the speed of light in that
substance.
Disadvantages
 Interfacing costs Fiber Types
 Strength  Plastic Core and Cladding
 Remote electrical power  Glass Core with Plastic Cladding (PCS)
 Specialized tools, equipment, and training  Glass Core and Glass Cladding (SCS)

Wave Nature of Light Mode of Propagation

Light is an electromagnetic wave having a Mode means path or ways light may travel into the optical fiber.
Very high oscillation frequency and a very short wavelength. • Single-mode
Infrared • Multi-mode
Visible light
Ultraviolet Index Profile
The graphical representation of the value of the refractive
Fiber Optic Window index across the fiber.
There are ranges of wavelengths at which the fiber operates
best. Each range is known as an operating window. Step Index Optical Fiber
 A fiber with a core with uniform
Window Operating Wavelength refractive index.
800 nm – 900 nm 850 nm  The core is surrounded by an
1250 nm – 1350 nm 1310 nm outside cladding with uniform
1500 nm – 1600 nm 1550 nm refractive index less than that of the
core.
These wavelengths are chosen because they best match the
transmission properties of available lights sources with the
transmission qualities of optical fiber.

1|Page
Prepared by: Engr. Rex Jason H. Agustin
LPU-Cavite
FAITH COLLEGES Fiber Optics
Graded Index Optical Fiber
 There is no cladding and the P  Pt x 10  Al /10
refractive index of the core is non-
uniform.
 The refractive index at the core is P = measured power level (Watts)
highest at the center and decreases Pt = Transmitted power level (Watts)
gradually with distance toward the A = cable power loss (dB/Km)
outer edge. l = cable length (Km)

Absorption Losses
 It is analogous to power dissipation in copper cable;
Optical Fiber Configurations  Impurities in the fiber absorb the light and convert it to
heat.
Single-mode Step Index  Ultraviolet Absorption
 Minimum dispersion  Infrared Absorption
 Wider bandwidth and high transmission rate  Ion Resonance Absorption

 Maximum Core Radius  Ultraviolet Absorption

 Core radius is proportional to the wavelength and  It is caused by valence electrons in the silica
the numerical aperture of the fiber. material from which the fibers are manufactured.
 Light ionizes the valence electrons into
0.383
rmax  conduction.
NA  Infrared Absorption
 It is the result of photons of light that are
 Cutoff-Wavelength absorbed by the atoms of the glass core
c  cutoff wavelength molecules.
dNA  The absorbed photons are converted to random
c  d  core diameter
2.405 mechanical vibrations typical to heating.
NA  numerical aperture  Ion Resonance Absorption
Multi-mode Step Index  Cause by OH ions in the material.
 Inexpensive and easy to manufacture  The ions are water trapped in the glass during
 Easier to couple light the manufacturing process.
 Also caused by iron, copper and chromium
Normalized Frequency molecules.
V = πd (NA) / λ
Chromatic or Wavelength Dispersion
Number of Modes It occurs when non-coherent light sources where light
#M = 0.5V2 contains combination of different wavelengths.
The different wavelengths have different velocities
Multi-mode Graded Index therefore do not arrive at the receiver at the same time.
 Compromise between Single Mode Step Index and It can be eliminated by using a monochromatic source.
Multimode Step Index. It can occur only in single mode of transmission.

Number of Modes Radiation Loss

#M = 0.25V2  Radiation Loss are predominantly caused by small bends
and kinks in the fiber.
Acceptance Angle
 It is the maximum angle in which  Microbends
external light rays may strike the  A microbend is a miniature bend or geometric
air-fiber interface and still propagate imperfection along the axis of the fiber which
down the fiber. represents the discontinuity in the fiber.
 Also called Acceptance Cone Half-  Microbending occurs as a result in differences in
Angle. the thermal contraction rates between the core
and the cladding material.
 Constant-Radius Bends
Acceptance Cone  These are caused by excessive pressure and
 Rotating the acceptance angle tension and generally occur when fibers are bent
around the fiber axis. during handling or installation.

Modal Dispersion
 Also known as pulse spreading.
 It is caused by the difference in the propagation times of
light ray that take different path down a fiber.
Numerical Aperture  It can occur only in multimode fibers.
 Closely related to Acceptance Angle.  In multimode propagation, dispersion is often expressed
 It is the Figure of Merit commonly used to measure the as BANDWIDTH DISTANCE PRODUCT.
magnitude of the acceptance angle.
 Described as the light gathering ability of an optical fiber. Coupling Losses
 Losses that occur in some types of optical junctions: Light-
NA  sin max
to-Source, Fiber-to-Fiber, and Fiber-to-Photodetector
NA  n12  n22 connections.

o Lateral Misalignment
Fiber Optics Losses o Gap Misalignment
o Angular Misalignment
Attenuation o Imperfect Surface Finish
Attenuation or Power Loss results in a reduction in the power
of the light wave as it travels down the cable.
2|Page
Prepared by: Engr. Rex Jason H. Agustin
LPU-Cavite
FAITH COLLEGES Fiber Optics
Optical Sources 4.) The following are the advantages of optical fiber system
except
Light-Emitting Diodes (LEDs) a.) Greater capacity
 A pn junction diode usually made up of AlGaAs or GaAsP. b.) Crosstalk immunity
 A spectral width of 30nm to 50nm is common with LEDs. c.) Safer to handle
d.) Lower initial cost of installation
LASERs
 Light Amplification by Stimulated Emission of Radiation. 5.) Plastic fibers have the following advantages over glass
 Theodore H. Maiman developed the FIRST LASER. fibers except
a.) Flexibility
Injection Laser Diode (ILD) b.) Ease of installation
 Similar to LED except that it operates in a higher threshold c.) Ruggedness
than LEDs. d.) Low attenuation
 5mW or 7 dBm is the typical output power.
 1 nm to 3 nm is the spectral Width of ILDs 6.) This explains how a light may react when it meets the
interface of two transmission materials that have different
Light Detectors indices of refraction.
a.) Huygens' Law
PIN b.) Nyquist's Theorem
 A depletion-layer photodiode. c.) Snell's Law
 A very lightly doped layer of n-type semiconductor material d.) Quantum Theory
is sandwiched between the junction a two heavily doped n
and p type materials. 7.) In Optical fibers,
a.) The core and cladding have the same index of refraction
APD b.) The core and cladding have the same area
 A PIPN structure. c.) The core surrounds the cladding
 Are more sensitive than PIN diodes and requires less d.) The cladding surrounds the core
amplification.
8.) A type of fiber whereby light rays take many paths between
Light Detectors Characteristics the source and the receiver.
a.) Monomode
Responsivity b.) Multimode
 It is the measure of conversion efficiency of a c.) Single mode
photodetector. d.) Step index
 It is the ratio of the output current of photodiode to the
input optical power and has a unit of amperes/watt. 9.) A figure of merit used to measure the light gathering or light
collection ability of the optical fiber.
Dark Current a.) Acceptance angle
 It is the leakage current that flows through a photodiode b.) Numerical aperture
with no light input. c.) Acceptance cone
d.) Critical angle
Transit Time
 It is the time it takes a light-induced carrier to travel across 10.) The basic optical fiber communications system consists of
the depletion region. the following except
a.) Optical source
Spectral Response b.) Photodetector
 It is the range of wavelength values that can be used for a c.) Transmission medium
given photodiode. d.) 48 v power supply
 800 nm to 820 nm is the wavelength range where
photodiode can efficiently absorb energy. 11.) Optical fibers can be made out of
a.) Glass
Light Sensitivity b.) Plastic
 It is the minimum optical power a light detector can receive c.) Combination of both
and still produce a usable electrical output signal. d.) Any of these

REVIEW QUESTIONS 12.) In ________, the core has an index of refraction that
changes continuously from the center to the outside.
1.) A transparent material along which we can transmit light is a.) Step index
called b.) Graded index
a.) Fiber optics c.) Monomode
b.) Flashlight d.) Multimode
c.) An optic fiber
d.) Xenon bulb 13.) The following are causes of attenuation and loss of optical
power within the fiber except
2.) A simple fiber optic system would consist of a.) Microbending loss
a.) A light source, an optic fiber and a photoelectric cell b.) Connector loss
b.) A laser, an optic fiber and an LED c.) Splicing loss
c.) A copper coaxial cable, a laser and a photoelectric cell d.) Ohmic loss
d.) An LED, a CRT and a light source
14.) For a signal to be propagated through the optical fiber, the
angle of incidence should be________ the critical angle.
3.) Optic fiber is normally made from a.) Greater than
a.) Coherent glass and xenon b.) Less than
b.) Copper c.) Equal to
c.) Water d.) None of these
d.) Silica glass or plastic

3|Page
Prepared by: Engr. Rex Jason H. Agustin
LPU-Cavite
FAITH COLLEGES Fiber Optics
15.) A ray of light in a transparent material of refractive index 25.) The maximum angle in which external light rays may strike
1.5 is approaching a material with a refractive index of 1.48. At the air fiber interface and still propagate down the fiber
the boundary, the critical angle is a.) Critical angle
a.) 90 degrees b.) Acceptance angle
b.) 9.4 degrees c.) Numerical aperture
c.) 75.2 degrees d.) Beamwidth
d.) 80.6 degrees
26.) Which of the following combinations is impossible for
16.) The first material has a refractive index of 1.51 and the optical fibers?
angle of incidence is 38 degrees and the second material has a.) Plastic core and cladding
a refractive index of 1.46. What is the angle of refraction? b.) Glass core and cladding
a.) 30.55 degrees c.) Plastic core and glass cladding
b.) 39.55 degrees d.) Glass core and plastic cladding
c.) 75.2 degrees
d.) 40.55 degrees 27.) The scientist who coined the term "Fiber Optics"
a.) Hopkins
17.) If the refractive index of the core of an optic fiber was 1.47 b.) Hansel
and that of the cladding was 1.44,the cone of acceptance c.) Kapany
would have an angle of approximately d.) Van Heel
a.) 17.19 degrees
b.) 72.82 degrees 28.) A technology for carrying many signals of different
c.) 78.4 degrees capacities through a synchronous, flexible optical hierarchy.
d.) 34.36 degrees a.) PDH
b.) SDH
18.) In free space, light travels at approximately c.) SONET
a.) 186000 m/sec d.) ATM
b.) 3 x 10exp9 m/sec
c.) 300 m/sec 29.) Two digital signals whose transmission occur at almost the
d.) 0.3m/nsec same rate are
a.) Plesiochronous
19.) Scattering loss is caused by b.) Synchronous
a.) Insufficient stirring of the ingredients during manufacture c.) Asyncronous
b.) Changes in the density of the fiber due to uneven rates of d.) Mesochronous
cooling
c.) Microscopic cracks in the cladding which allow leakage of 30.) SONET systems are
the vacuum in the core a.) Twisted pair copper based technology
d.) Impurities in the fiber b.) Fiber optic technology
c.) Hybrid fiber coax technology
20.) Cleaving is the process of d.) Wireless technology
a.) Removing the cladding before connecting fibers together
b.) Cutting the end of the fiber in preparation for connecting
two fibers TO GOD BE THE GLORY!
c.) Cleaning the surface of optic fibers
d.) Inspecting fibers for flaws

21.) A typical value of insertion loss for a mechanical splice

a.) -50 dB
b.) 0.2 dB
c.) 12 mm
d.) 3 dB

22.) The speed of light in a transparent material

a.) Is always the same regardless of the material chosen
b.) Is never greater than the speed of light in free space
c.) Increases if the light enters a material with a higher
refractive index
d.) Is slowed down by a factor of 1 million within the first 60
meters

23.) The following are light detectors in fiber optic

communications system except
a.) ILD
b.) PIN diode
c.) APD
d.) None of these

24.) The following are three distinct regions of an optical fiber

except
a.) Core
b.) Cladding
c.) Spacers
d.) Coating

4|Page
Prepared by: Engr. Rex Jason H. Agustin