PHY110 – ENGINEERING PHYSICS
UNIT 1. Electromagnetic theory CA1- Lab@Home
UNIT 2. Lasers and Applications
Class test 1 (CA2)
UNIT 3. Fiber optics
MTE- MCQ ( Unit 1 to 3)
UNIT 4. Quantum mechanics
UNIT 5. Solid State Physics
Class test 2 (CA3) - Online assignment
UNIT 6. Introduction to engineering materials
ETE- MCQ
Reji Thomas DRD-DRC March 1, 2023
PHY109 UNIT III: Fiber optics
2
LECTURE 1
Cable
1926-2020
The term ‘fiber optics’ was coined by Indian-American physicist Narinder
Singh Kapany, who is widely acknowledged as the father of fiber optics.
He was awarded India's Second highest civilian award the Padma
Vibhushan in 2021.
Prof. Reji Thomas DRD-DRC March 1, 2023
FIBER OPTICS
3
We can’t live without the INTERNET, and
hence we can’t avoid OPTICAL FIBER
How many km of fiber optic cables are used
in LPU for networking ??
Understand fiber optics and why they are important- We
will learn in this UNIT III
https://www.youtube.com/watch?v=x3c1ih2NJEg
Prof. Reji Thomas DRC-DRD March 1, 2023
4
Which type of laser is the simplest to modulate directly by changing
its excitation?
a. Semiconductor
b. Ruby
c. Helium-neon
d. Neodymium-YAG
Ans: A
Prof. Reji Thomas DRC-DRD March 1, 2023
Historical Developments
5
1870 John Tyndall guided light through water air interface – He explained
first why the sky is blue!
1950 Hopkins and Narinder Singh Kapany realized transmission of images
through optical fiber. It was Kapani, an Indian origin scientist coined the
name Fiber Optics..
1960 light transmitted through glass.. But that glass was lossy..
1966 Kao and Hockham proposed information transmission over fiber..
1970 Corning Glass developed low loss optical fiber transmission lines.
Semiconductor laser revolutionized information transmission
https://www.youtube.com/watch?v=0MwMkBET_5I&feature=emb_title
The sky appears blue because
a) ocean is blue
b) It is due to the process of scattering.
c) Due to Rayleigh scattering (1/ 4)
d) Long wavelength light, including red, orange and yellow are
scattered more by atmospheric particles
e) Short wavelength light, including violet, indico and blue are
scattered less by atmospheric particles
Ans: B to E
Within the visible range of light, red light waves are scattered
the least by atmospheric gas molecules
6
Prof. Reji Thomas DRC-DRD March 1, 2023
7
And why does a sky change colors during sunset and
sunrise?
a. When the sunlight travels a long path through the atmosphere to
reach our eyes, the blue light has been mostly removed
b. Particles that are small compared with the light wavelength
scatter blue light more strongly than red light.
c. All of the above
d. None of the above Ans: C
Prof. Reji Thomas DRC-DRD March 1, 2023
FIBER OPTICS
“Fiber optics is a technology in which electrical signal is converted to
optical signals and transmitted through fibers and reconverted back into
electrical signals”
1977- Commercial communication system based on Optical fibers
came into existence based on the proposed information
transmission over glass fiber by Charles Kao (2009 Nobel
Prize winner) and George Hockham.
LASER diode and LED revolutionized the
communication sector, which was dominated by
Microwave and Radio waves as the carrier waves for
sending information..
Use of light as carrier wave improved the bandwidth
considerably Prof. Reji Thomas DRC-DRD March 1, 2023
9
From the following list, which laser emits radiation in the
visible range i.e., 400 to 700 nm?
a. Argon-ion
b. Nitrogen
c. Carbon-dioxide
d. Neodymium-YAG
Ans: A
Prof. Reji Thomas DRC-DRD March 1, 2023
10
Which is the proper measurement of average power
emitted by a pulsed laser?
a. Energy x time
b. Pulse energy x repetition rate
c. Pulse energy / repetition rate
d. Peak power x pulse length
Ans: C
Prof. Reji Thomas DRC-DRD March 1, 2023
11
Which of the following contributes to the broadening of laser
emission bandwidth?
a. Doppler shift of moving atoms and molecules
b. Amplification within the laser medium
c. Coherence of the laser light
d. Optical pumping of the laser transition
Ans: A
Prof. Reji Thomas DRC-DRD March 1, 2023
UNIT III: Fiber optics
Syllabus
Fiber optics introduction, optical fiber as a dielectric wave guide,
total internal reflection, acceptance angle, numerical aperture,
relative refractive index, V-number, step index and graded index
fibers, losses associated with optical fibers, application of optical
fibers.
So it is all about basics of Fiber Optics and its application.
Prof. Reji Thomas DRC-DRD March 1, 2023
Fiber optics
Lecture 1: 1/03/23 Fiber optics introduction, optical fibers, optical fiber as a
dielectric wave guide, Total internal reflection
Lecture 2: 3/03/23, Acceptance angle, relative refractive index, numerical
aperture, Classification of fibers, Step index and graded index fibers,
V-number, and modes of propagation
Learned the fundamentals of optical fiber, the fundamental parameters of optical
fibers and propagation of light through optical fiber, learned about
the types of fibers
Lecture 3: 7/03/23; Losses associated with optical fibers; learn the reason for data
loss
Lecture 4: 10/03/23 Application of optical fibers.
Prof. Reji Thomas DRC-DRD March 1, 2023
Optical Fiber System
Laser diode/LED Photo diode
OPTICAL FIBER SYSTEM
“Fiber optics is a technology in which electrical signal is
converted to optical signals and transmitted through fibers and
reconverted back into electrical signals”
Prof. Reji Thomas DRC-DRD March 1, 2023
Optical Fiber
An optical fiber is a thin strand of dielectric material (glass or
plastic) that can carry light from one end to the other,
• Light undergoes total internal reflection (n1>n2)
• Zig-Zag path
n =1 • Launching /acceptance angle
AIR 2 • Small attenuation
n1 n2=1 • Will travel over the bends as well
AIR
Thin strand of dielectric material we call fiber (transmission of
light) where as if it is of metal we call it a wire (transmission of
electrical signal)
Prof. Reji Thomas DRC-DRD March 1, 2023
16
A dielectric waveguide for the propagation of electromagnetic
energy at light frequencies
a. Stripline
b. Microstrip
c. Laser beam
d. Optical fiber
Ans: D
Prof. Reji Thomas DRC-DRD March 1, 2023
Optical Fiber
Structure: Human hair thickness ~ 100µm
1. Core - Light guiding region
2. Cladding- confine the light to the core
3. Buffer or Sheath - protect the fiber from physical and
environmental damage
Prof. Reji Thomas DRC-DRD March 1, 2023
Functions of ‘Cladding’ in Optical fiber
Why cladding is necessary?
i. To maintain the uniformity along the length of the fiber
a) Make the diameter of the core remain constant and ensure same medium around the
core
ii. To protect the outer surface of the core
a) Ensure a scratch and dust free core surface along with immunity for
environmental changes and physical damage (chipping).. Loss reduced
b) Easier to add other protective layers over the fiber
iii. To reduce the cone of the light
a) Ensure higher bit rate of transmission
iv. To confine light to the core
a) Make sure the condition for total internal reflection always met along the length;
maintain the signal strength
b) Allows to pack the fibers in bundles by insulating it from other fibers in close
proximity.
Prof. Reji Thomas DRC-DRD March 1, 2023
OPTICAL FIBER CABLE
Single Fiber cable (side view)
Multi Fiber cable (cross section)
Prof. Reji Thomas DRC-DRD March 1, 2023
Optical fiber as a dielectric wave guide
Light propagate through an Optical fiber as an electromagnetic
wave
Propagation governed by Maxwell’s equations /wave equations
r= n2 at optical
frequency
Light waves in free space are transverse electromagnetic
(TEM) waves
In Optical fiber light is guided and hence a different
electromagnetic field configurations, either transverse
electric (TE) mode or transverse magnetic (TM) mode or
hybrid mode.
Prof. Reji Thomas DRC-DRD March 1, 2023
21
A Fiber optic telephone transmission can handle more
than thousands of voice channels. True or false?
(a) True
(b) False
Ans: A
Prof. Reji Thomas DRC-DRD March 1, 2023
22
The core of an optical fiber has a
a. Lower refracted index than air
b. Lower refractive index than the cladding
c. Higher refractive index than the cladding
d. Similar refractive index with the cladding
Ans: C
Prof. Reji Thomas DRC-DRD March 1, 2023
23
Which of the following is used as an optical transmitter on
the Fiber Optical Communications?
a. Avalanche Photo Diode (APD)
b. Limited Space Accumulation diode (LSA diode)
c. P type-Intrinsic-N type diode(PIN diode)
d. Light emitting diode (LED)
Ans: D
Prof. Reji Thomas DRC-DRD March 1, 2023
24
Which of the following is used as an optical receiver in fiber optics
communications?
a. Avalanche Photo Diode (APD)
b. Tunnel diode
c. Laser diode
d. LED
Ans: A
Prof. Reji Thomas DRC-DRD March 1, 2023
Total Internal Reflection
Rarer medium n2 < n 1
n2
n1
Denser medium n1 > n 2
Eq.1
When a ray of light incident on the interface from a denser
medium, the refracted ray bend away from the normal in the rarer
medium. In that case the angle of incidence and refraction are
related to refractive indices n1 (denser medium) and n2 (rarer
medium) through Snell’s law
Prof. Reji Thomas DRC-DRD March 1, 2023
Total Internal Reflection
n2
n2
n1
n1
Reflected ray
According to Eq.1, as incident angle (1) increases refracted angle (2) also increases
Means refracted ray move more and more away from the normal
When 1 becomes c , (critical angle )refracted ray just glide the interface 2 =90°
Prof. Reji Thomas DRC-DRD March 1, 2023
Total Internal Reflection
In the third case, when incident angle 1 > c there is no refracted ray into rarer
medium. The ray is reflected back to denser medium as if it encountered specular
reflection
n2 n2
n2
n1
n1
n1 Reflected ray
Reflected ray
1 > c ; Specular reflection?
To summarize
i. 1 < c , Ray of light refract to rarer medium
ii. 1 = c. Ray of light grazes the interface of rare-denser medium
iii. 1 > c, Ray of light totally reflect back into denser medium
Prof. Reji Thomas DRC-DRD March 1, 2023
28
What is the principle of fiber optical communication?
a) Frequency modulation
b) Population inversion
c) Total internal reflection
d) Doppler Effect
Ans: C
Prof. Reji Thomas DRC-DRD March 1, 2023
29
Snell’s law describes
a) Interference
b) Diffraction
c) Refraction
d) Reflection
Ans: C
Prof. Reji Thomas DRC-DRD March 1, 2023
Fiber optics
Lecture1: 1/03/23 Fiber optics introduction, optical fibers, optical fiber as a
dielectric wave guide, Total internal reflection
Lecture 2: 3/03/23, Acceptance angle, relative refractive index, numerical
aperture, Classification of fibers, Step index and graded index
fibers, V-number, and modes of propagation
Learned the fundamentals of optical fiber, the fundamental parameters of optical
fibers and propagation of light through optical fiber, learned about
the types of fibers
Lecture 3: 7/03/23 Losses associated with optical fibers; learn the reason for data
loss
Lecture 4: 10/03/23 Application of optical fibers in computer networking and
broadcasting
Prof. Reji Thomas DRC-DRD March 1, 2023
31
Prof. Reji Thomas DRC-DRD March 1, 2023
