INTRODUCTION TO FIBER OPTIC.pdf

FIBER OPTIC COMMUNICATION SYSTEM
DEP40053 1
DEP40053_Hanisah/JKE/PTSS

FIBER OPTIC COMMUNICATION SYSTEM introduces students
to the basic concept of fiber optic in communication systems with
environmental sustainability. This course covers fiber optic
characteristics, components in fiber optic system, losses in fiber
optic cable and the fundamental concept of optical measurement.
This course also provides knowledge in splicing techniques with
safety awareness, multiplexing techniques and design
consideration in fiber optic communication link.
SYNOPSIS
2

FIBER OPTIC CHARACTERISTICS
CHAPTER 1
3

1. Remember fiber optic
2. Understand the fiber optic communication system concepts
3. Remember properties of the light, optical law and the transmission losses in
fiber optic cables
4. Apply index of refraction formula
5. Investigate Snell’s Law to determine the characteristics of light propagation
6. Investigate the construction of fiber optic cable
7. Understand modes and index profiles
8. Understand type of fiber optic cable
4
CHAPTER 1: FIBER OPTIC CHARACTERISTICS

• Optical fiber is a transmission medium to send signals from one location to
another in the form of light guided through thin fibers of glass or plastic.
• These signals are digital pulses or continuously modulated analog (PCM,
PAM, PWM..) streams of light representing information.
• These can be audio/text/image/video/data information or any other type
of information.
5
INTRODUCTION

1. CONSUME LESS ENERGY
• Fiber optic cable systems save more energy than copper cable systems.
• Fiber can transmit more data over longer distances but still use less energy than copper.
• For example, coaxial cables consume 3.5 W to transmit data over 100 m, while fiber optic
systems just use even less than 1 W to conduct light pulses over 300 m.
• With less energy use, carbon dioxide emissions can also be reduced.
2. LESS GENERATE HEAT
• Less energy means less generated heat, therefore fiber optic cables don’t need cooling
systems to cool down the data and keep it at an appropriate temperature.
• This means that less air conditioning tools are needed, saving equipment and floor space.
ENVIROMENTAL BENEFITS OF FIBER OPTIC IN COMM
SYSTEM
6
Here are three reasons why fiber-optic technology can be considered a “green” technology:

3. REQUIRE FEWER MATERIALS
• Fewer materials are required to build fiber-optic cables than copper cables.
• A fiber-optic cable uses less insulation and jacketing.
• Additionally, fiber-optic cables have a longer lifespan than copper cables. This is
because fiber is more durable than copper.
• With a longer lifespan, fewer fiber cables are pulled out of the ground and thrown away.
• Therefore, fewer materials are used because fiber-optic materials do not need to be built
and installed as frequently.
ENVIROMENTAL BENEFITS OF FIBER OPTIC IN COMM
SYSTEM
7
Here are three reasons why fiber-optic technology can be considered a “green” technology:

(1) CODER
9
• It is a ADC (analog to digital converter).
• Coder converts input analog information signals (such as audio, video) into digital signals.
• If the input signals are in digital (computer data), they are directly connected to light source
transmitter circuit.
audio, video or
computer data
TRANSMITTER SECTION

(2) LIGHT SOURCE
• Light source is a transducer that convert the digital pulses of electrical current into light pulses.
• Two types: - Focus type LED (Light Emitting Diode)
- Low intensity laser beam such as Injection Laser Diode (ILD)
• The frequency of digital pulses control the rate, at which light source turns ON/OFF.
TRANSMITTER SECTION
10

(3) FIBER OPTIC CABLE (FOC)
• FOC transmit the light-beam pulses from one end of fiber optic cable to the other end.
• Advantages: - Has very less attenuation(loss due to absorption of light waves) over a long
distance.
- Has large bandwidth (BW); hence, its information carrying capacity is high.
TRANSMISSION MEDIUM SECTION
11

(4) PHOTO DETECTOR / LIGHT DETECTOR
• Photodetector is a transducer that detect the light pulses and then converts it into electrical
signal pulses.
• The electrical signal pulses are then amplified by amplifier circuit.
• and reshaped into original digital pulses by the shaper circuit.
RECEIVER SECTION
12

(5) DECODER
13
• It is a DAC (digital to analog converter).
• Decoder converts digital signals into analog signals (such as audio, video)
• If the output are required in digital signals (computer data), the signal can be directly taken out
from the shaper circuit without go through the decoder.
RECEIVER SECTION
0V
5V
Pulses after
shaper
process

LIGHT PROPAGATION
• This electromagnetic energy consists two components which are electric field, E and
magnetic field, H which oscillate and perpendicular each other as shown in Figure 1.
15
WHAT IS LIGHT? LIGHT is a kind of electromagnetic radiation
that has very short wavelength

LIGHT PROPAGATION
• A wave has a wavelength (λ) , frequency (f ), period (T) and velocity (ν) as shown in
Figure 2.
• In fiber optics communication systems, one of the important parameter is wavelength.
Therefore, following properties can be defined for light wave;
16
1 cycle
1 wavelength
1 period
A
Figure 2 : Wave Light

LIGHT PROPAGATION
• Wavelength (λ) - is the length of wave in one cycle distance OR
distance between two crests. (Unit: meter, m)
• Frequency (f) - How often cycle of wave repeats in one second OR
number of cycles per second. (Unit: Hertz, Hz)
• Period (T) - the duration of one cycle of wave. It is reciprocal of
frequency. (Unit: second, s)
• Velocity (v) – the distance covered by the wave in one second.
(Unit: m/s)
• Crest and Trough (A) - the distance from midline to peak of wave.
Amplitude is a measure of the intensity or brightness of light
radiation. The increase of amplitude will increase intensity of light.
17
𝑻 =
𝟏
𝒇
=
𝝀
𝒗
𝒗 =
𝒄
𝒏
𝝀 =
𝒄
𝒇
=
𝒗
𝒇

LIGHT PROPAGATION
• The velocity of light wave is not constant. It depends on type of medium the wave
travels through.
• The velocity of light wave in free space(or vacuum) is constant and denoted by c
where c = 3 x 108 m/s.
• However in Fiber optic cable, the speed of light, v will be downgraded since the
fiber optic is made from glass or plastic.
• The speed of light will decrease when light travels in non-vacuum transparent
media such as air, glass, water, oil, fiber (air – 0.03% slower, glass – 30% slower)
• The relationship among wavelength (λ), frequency(f) and velocity of light (c or v) is
expressed mathematically as:
18
𝝀 =
𝒄
𝒇
=
𝒗
𝒇 ….. equation 1.1

LIGHT PROPAGATION
• From equation 1.1, it can be seen that wavelength (λ) is inversely proportional to
the frequency (f).
• high frequency = short wavelength
• low frequency = long wavelength
19
𝝀 =
𝒄
𝒇
=
𝒗
𝒇 ….. equation 1.1
Where;
c = speed of light in free space = 3 x 108 (m/s)
v = speed of light in any transparent medium (m/s)
λ = wavelength (m)
f = frequency (Hz)

ELECTROMAGNETIC FREQUENCY SPECTRUM
20
• Light is a kind of electromagnetic radiation, hence it is part of the Electromagnetic
Frequency Spectrum.
104 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016
105 104 103 102 10 1 10-1 10-2 10-3 10-4 10-5 10-6 10-7
VLF LF MF HF VHF UHF SHF EHF IR UV
VR
Telephone
Lines
AM Radio Broadcast TV
Satellite
Downlink
Fiber Optic
Wavelengths
Visible
Light
Fiber optic transmission wavelengths

LIGHT FREQUENCY SPECTRUM
21
Visible
Band of light wavelengths to
which the human eye will
respond.
Ultraviolet
Band of light wavelengths
that are too short to be
seen by the human eye.
Infrared
Band of light wavelengths
that are too long to be
seen by the human eye.
Light frequency spectrum can be divided
into three general bands:

LIGHT FREQUENCY SPECTRUM
22
Different wavelength or frequency
will give different color of light
wave as shown in Table 1.
Table 1

VISIBLE LIGHT FREQUENCY SPECTRUM
23
Visible Light range is estimated from 740 nm to 380 nm

FIBER OPTIC FREQUENCY SPECTRUM
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Band Description Wavelength Range
O band original 1260 to 1360 nm
E band extended 1360 to 1460 nm
S band short wavelengths 1460 to 1530 nm
C band
conventional
("erbium window")
1530 to 1565 nm
L band long wavelengths 1565 to 1625 nm
U band
Ultra long
wavelengths
1625 to 1675 nm

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ATTENUATION, WAVELENGTH & TRANSMISSION WINDOW
• Fiber Attenuation is caused by scattering, absorption and bending of cable.
• Scattering (often referred to as Rayleigh scattering) is the reflection of small amounts of
light in all directions as it travels down the fiber.
• Transmission window : is where optical attenuation is low

26
Window Range
Operating
Wavelength
First Window 800 nm – 900 nm 850 nm
Second Window 1260 nm – 1360 nm 1310 nm
Third Window 1500 nm – 1600 nm 1550 nm
• According to attenuation-wavelength graph, there are three wavelength windows that has low
attenuation : 850 nm, 1310 nm and 1550 nm windows.
• Therefore, Infrared Light with wavelengths of 850 nm, 1310 nm and 1550 nm are mostly used.
• Light Emitting Diode (LED) and Laser Diode (LD) are most common light sources that has been
used since they operate in infrared radiation (750 nm to 1 mm).
ATTENUATION – WAVELENGTH CURVE

WAVELENGTH USED IN FIBER OPTIC
27
• There are three (3) wavelength are used in Fiber
optic communication system due to low
attenuation;
λ = 850 nm, 1310 nm, 1550 nm
• The frequency around 850 nm has higher losses
and it is used for shorter range data
transmissions and local area networks (LANs),
perhaps up to 10 km or so.
• However, 850 nm window remains in use
because of the system is less expensive and
easier to install.

OPTICAL FIBER PROPERTIES
28
• Light has different phenomena/behavior when it interact with other objects such as;
Reflection – The rays of light can be reflected off the object.
Refraction - The rays of light can be refracted through the object.
Pass Through - The rays of light can pass through the object
Scattering - The rays of light can be scattered off the object.
Absorption - The rays of light can be absorbed by the object.

OPTICAL FIBER PROPERTIES
29
• Light has different phenomena/behavior when it interact with other objects such as;
Diffraction - The rays of light can diffract through single slit of the
object
Interference – The rays of light can be interfered each others after
pass through 2 or more slits.
Polarization - The rays of light can be polarized by the polarizer.

30
DIFFRACTION
(a) Pinhole Diffraction
(b) Single Slit
Diffraction (c) Straight Edge
Diffraction
DIFFRACTION is the spreading of waves as it moves around the edge of an obstacle or
passes through a narrow opening.
Diffraction occurs when light waves pass through small openings, around obstacles, or
by sharp edges.
The light that passes through the opening is partially redirected due to an interaction with
the edges.

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INTERFERENCE
Constructive
Interference
occurs when crest
meet crest.
Destructive
Interference occurs
when crest meet
trough
INTERFERENCE is the phenomenon produced by the superposition of waves from two
or more coherence sources.
Interference can either be constructive, meaning the strength (light intensity)
increases as result, or destructive where the strength (light intensity) is reduced.

Law of Reflection: The angle of incidence, θi (from NL to ray) is equivalent
to the angle of reflection, θr.
32
θi θr
REFLECTION is the return of the light ray into the medium from which it
originated when it hit the reflecting surface between two different media.
v1
v1
λ1
λ1
REFLECTION
θi = θr
Normal Line

33
θ1
θ2
n1
n2
REFRACTION is the bending of light ray when light ray moves from one
medium to another medium of different optical density, n.
θ1
θ2
n1
n2
v1
v2
λ1
λ2
Refraction occurs as a result of the change of the speed of light, v when light
travels from one medium to another difference medium obliquely.
Normal Line
REFRACTION

The index of refraction or
optical density (n) of a
material is the ratio of the
speed of light (c) in a
vacuum to the speed of
light in the material (v)
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SUBSTANCE INDEX OF REFRACTION, n
Solids at 20 °C
Diamond 2.419
Glass, crown 1.523
Ice (0°C) 1.300
Sodium chloride 1.544
Crystalline Quartz 1.544
Fused Quartz 1.458
SUBSTANCE INDEX OF REFRACTION, n
Liquids at 20 °C
Benzene 1.501
Carbon disulfide 1.632
Carbon tetrachloride 1.461
Ethyl alcohol 1.362
Water 1.333
INDEX OF REFRACTION (n)

• From equation it can be seen that refractive index (n) is inversely proportional
to the velocity of light (v) in certain medium.
• Low refractive index = high velocity
• High refractive index = low velocity
• For example, calculate the speed of following medium;
35
INDEX OF REFRACTION (n)
𝑛 =
𝑐
𝑣
Medium Refractive Index, n Speed of Light, v
Air 1.0003
Water 1.333
Perspex 1.49
Glass 1.5
As conclusion, different medium will refract light at different amount because
different medium has different refractive index, n and speed, v

QUESTION 1
Given the index of refraction of diamond is 2.419 and the velocity of light in a vacuum is
3 x 108 m/s. Calculate the velocity of light in the material?
QUESTION 2
Given the velocity of light in water is 2.248 x 108 m/s, and the velocity of light in a vacuum is
3 x 108 m/s. Calculate the index of refraction of the material?
QUESTION 3
Given the index of refraction of diamond is 2.419, crystalline is 1.544, benzene 1.501 and
the velocity of light in a vacuum is 3 x 108 m/s. Calculate the velocity of light in all three
material?
QUESTION 4
Optical fibers, which are constructed from plastic and glass, have a refractive index of 1.48
and 1.6. Calculate the speed of light of each material. Give your opinion on which
material is the core.
36
EXERCISE

2.419 =
3 x 108 m/s
𝑣
𝑣 =
3 x 108 m/s
2.419
𝒗 = 𝟏. 𝟐𝟑𝟔 𝒙 𝟏𝟎𝟖m/s
SOLUTION
37
𝑛 =
𝑐
𝑣
QUESTION 1
Given the index of refraction of diamond is 2.419 and the velocity of light in a vacuum is 3 x 108
m/s. Calculate the velocity of light in the material?
QUESTION 2
Given the velocity of light in water is 2.248 x 108 m/s, and the velocity of light in a vacuum is 3 x 108
m/s. Calculate the index of refraction of the material?
SOLUTION
𝑛 =
𝑐
𝑣
3 x 108 m/s
𝑛 =
2.248 x 108 m/s 𝒏 = 𝟏. 𝟎𝟏𝟗

SOLUTION
38
QUESTION 3
Given the index of refraction of diamond is 2.419, crystalline is 1.544, benzene 1.501 and the
velocity of light in a vacuum is 3 x 108 m/s. Calculate the velocity of light in all three material?
index of refraction of
diamond = 2.419
index of refraction
of benzene = 1.501
𝑛 =
𝑐
𝑣
𝑣 =
3 × 108
2.419
𝒗 = 𝟏. 𝟐𝟑𝟔 × 𝟏𝟎𝟖𝒎/𝒔
𝑣 =
3 × 108
1.501
𝒗 = 𝟏. 𝟗𝟗𝟐 × 𝟏𝟎𝟖𝒎/𝒔
𝑛 =
𝑐
𝑣
index of refraction
of crystalline = 1.544
𝑛 =
𝑐
𝑣
𝑣 =
3 × 108
1.544
𝒗 = 𝟏. 𝟗𝟑𝟕 × 𝟏𝟎𝟖
𝒎/𝒔

SOLUTION
39
QUESTION 4
Optical fibers, which are constructed from plastic and glass, have a refractive index of 1.48 and 1.6.
Calculate the speed of light of each material. Give your opinion, which material is the core?
Refractive index of 1.48
𝑛 =
𝑐
𝑣
𝑣 =
3 × 108
1.48
𝒗 = 𝟐. 𝟎𝟐𝟕 × 𝟏𝟎𝟖𝒎/𝒔
Refractive index of 1.6
𝑛 =
𝑐
𝑣
𝑣 =
3 × 108
1.6
𝒗 = 𝟏. 𝟖𝟕𝟓 × 𝟏𝟎𝟖
𝒎/𝒔

QUESTION 5
Calculate wavelength of 480 THz of red light in medium
i. free space (n = 1.00)
ii. Air (n = 1.0003)
iii. Glass (n = 1.55)
40
EXERCISE
SOLUTION
i. free space (n = 1.00) ii. Air (n = 1.0003) iii. Glass (n = 1.55)
𝜆 =
𝑐
𝑓
=
𝟑 × 𝟏𝟎𝟖
𝒎/𝒔
480𝑇
= 𝟔𝟐𝟓 𝒏𝒎
𝑣𝑎𝑖𝑟 =
𝑐
𝑛𝑎𝑖𝑟
=
3 × 108
1.0003
= 𝟐. 𝟗𝟗𝟗𝟏 × 𝟏𝟎𝟖
𝒎/𝑠
𝜆 =
𝑣𝑎𝑖𝑟
𝑓
=
2.9991 × 108
480𝑇
= 𝟔𝟐𝟒. 𝟖 𝒏𝒎
𝑣𝑔𝑙𝑎𝑠𝑠 =
𝑐
𝑛𝑔𝑙𝑎𝑠𝑠
=
3 × 108
1.55
= 𝟏. 𝟗𝟑𝟓𝟓 × 𝟏𝟎𝟖
𝒎/𝒔
𝜆 =
𝑣𝑔𝑙𝑎𝑠𝑠
𝑓
=
1.9355 × 108
480𝑇
= 𝟒𝟎𝟑. 𝟐𝟑 𝒏𝒎

41
SNELL’S LAW – Refraction Law
Snell’s Law state that “the ratio of the sines of the incident angle and sines of the
refraction angle is equivalent to the ratio of velocities OR equivalent to the reciprocal
ratio of refractive index in the two media”
Snell’s Law is applied for REFTRACTION only

42
TWO Difference Cases of REFRACTION
CASE 1 (n1 < n2)
• When the light travels from a less dense
medium (small refractive index) to a denser
medium (larger refractive index), the light will
bends towards the normal line.
• The refraction angle 2 is smaller than incident
angle 1 (2 < 1)
Air
Glass
n1
n2
CASE 2 (n1 > n2)
• When the light travels from a denser medium
(larger refractive index) to a less dense medium
(small refractive index) ,the light will bends away
from the normal line.
• The refraction angle 2 is greater than incident
angle 1 (2 > 2)
Glass
Air
What happen if we increase the angle of incident further??

43
CRITICAL ANGLE, θc
So, CRITICAL ANGLE is an incidence angle that produces an angle of
refraction of 90° ( θ1 = θc )
θ2 = 90°
When the angle of refraction is 90° (θ2= 90°), the
incidence angle, θ1 is not more called incidence angle
but CRITICAL ANGLE, θC
When light passes from a medium of larger refractive
index into one of smaller refractive index, the refracted
ray bends away from the normal line.
If the incident angle θ1 is increased further, the refraction
ray will move more away from the normal line until the
angle of refraction is 90° and the light is refracted along
the boundary between the two materials.

44
CRITICAL ANGLE, θc
θ2 = 90°
▪ Snell’s Law...
▪ If θ2 = 90°, then θ1 = θC
▪ Therefore;
𝒏𝟏 𝐬𝐢𝐧 𝜽𝑪 = 𝒏𝟐 𝐬𝐢𝐧 𝟗𝟎°
𝒏𝟏 𝐬𝐢𝐧 𝜽𝑪 = 𝒏𝟐 𝟏
𝐬𝐢𝐧 𝜽𝑪 =
𝒏𝟐
𝒏𝟏
𝜽𝒄 = 𝐬𝐢𝐧−𝟏
𝒏𝟐
𝒏𝟏
𝒏𝟏 𝐬𝐢𝐧 𝜽𝟏 = 𝒏𝟐 𝐬𝐢𝐧 𝜽𝟐
𝛉𝐜 = 𝐬𝐢𝐧−𝟏
𝐧𝟐
𝐧𝟏
What happen if we increase the angle of incident further??
Critical Angle,
core
cladding

45
TOTAL INTERNAL REFLECTION, TIR
If the angle incidence is increased
further, the light is not refracted any
more, but it will be internally reflected
which known as TOTAL INTERNAL
REFLECTION (TIR)
As a conclusion, TIR could occur if;
i. The light travels from a medium of larger
refractive index into one of smaller
refractive index medium. (ncore > ncladding)
ii. The angle of incidence must greater than
critical angle (θ1 > θc)

QUESTION 6
A light ray strikes an air/water surface at an angle of 46° with respect to the normal and
refractive index of water is 1.33 and air is 1.0003. Find the angle of refraction when the
direction of the ray is
i. from air to water
ii. from water to air
46
EXERCISE
SOLUTION
θ1 = 46°
Water
θ1 = 46°
Water
𝑛1 sin 𝜃1 = 𝑛2 sin 𝜃2
𝜃2 = sin−1
𝑛1 sin 𝜃1
𝑛2
𝜃2 = sin−1
1.0003 sin 46 °
1.33
= 𝟑𝟐. 𝟕𝟓°
n1
n2 n1
n2
from air to water,
𝜃2 = sin−1
𝑛1 sin 𝜃1
𝑛2
𝜃2 = sin−1
1.33 sin 46 °
1.0003
= 𝟕𝟑. 𝟎𝟑°
θ2
θ2
from water to air,
WHAT CONCLUSION YOU CAN
MAKE FROM THIS SOLUTION?

QUESTION 7
A light ray of wavelength 650 nm travelling through air is incident on a smooth, flat slab of
crown glass at an angle 30° to the normal. If the index refraction of the crown glass is 1.52,
calculate:
i. refraction angle
ii. speed of light in crown glass
47
EXERCISE
𝜃2 = sin−1
𝑛1 sin 𝜃1
𝑛2
𝜃2 = sin−1
1.0003 sin 30 °
1.52
= 𝟏𝟗. 𝟐𝟏°
θ1 = 30°
θ2 = 19.21°
n1 = 1.0003
n2 = 1.52
SOLUTION
i. Refraction angle ii. speed of light in crown glass
𝑣2 =
𝑐
𝑛2
=
3 × 108
1.52
𝑣2 = 197.368 × 106 𝑚𝑠−1
𝑣2 = 1.974 × 108
𝑚𝑠−1
v2 = 1.974 x 108 m/s
v1 = 2.9991 x 108 m/s

QUESTION 8
A light ray travels inside fiber optic cable from glass-core medium at speed
1.987 x 108 m/s into plastic-cladding medium at speed 2.068 x 108 m/s. Calculate;
i. Refractive index of glass-core
ii. Refractive index of plastic-clad
iii. Critical angle of glass-core
48
EXERCISE
( answ: n1 = 1.51, n2 = 1.451, θc = 73.93°)

49
ACCEPTANCE ANGLE, θa
θi = θa
θr
θ1= θc
air, n0
θ2= 90° Acceptance angle, θa is the maximum incidence
angle of a light ray at the interface between air and
core that enables light ray enters core and travel
along the fiber core.
Acceptance angle is an incidence angle at the air-
core that causes the incidence angle at the core-
cladding interface equals to critical angle, θ1= θc
The acceptance angle is related to Numerical aperture,
NA by equation:
𝛉𝒂 = 𝐬𝐢𝐧−𝟏 𝑵𝑨
Half of the angle of acceptance cone is called the acceptance angle

50
ACEPTANCE ANGLE, θa
Transmission of light when incident angle, θi is bigger than acceptance angle, θa (θi > θa)
θ1 < θc where θ1 = 90º - θr
θi > θa
When incidence angle θi is bigger than acceptance angle θa, the light ray will refract
and pass through the interface between core - cladding because θ1 < θc . This light may
travel in the cladding for a while but is eventually lost from the fiber.
θ2
REFRACTION
REFRACTION

51
When incidence angle θi is equal to acceptance angle θa, the light ray will enters
and travel along the fiber core-cladding boundary at critical condition where θ1 = θc
Transmission of light when incident angle, θi is equal to acceptance angle, θa (θi = θa)
θ1 = θc
where θ1 = 90º - θr
θi = θa
= θ2

52
When incidence angle θi is smaller than acceptance angle θa, the light rays are
totally internally reflected (TIR) at the boundary between the fiber's core and
cladding. As these rays propagate down the fiber, they remain trapped in the core.
Transmission of light when incident angle, θi is smaller than acceptance angle, θa (θi < θa)
where θ1 = 90º - θr
θ1 > θc
θi < θa
REFRACTION
TIR

53
θr
θ1 > θc
air, n0
θ2= 90°
i. Light travels from a medium that has larger
refractive index into medium of smaller
refractive index. (ncore > ncladding)
ii. Incident angle at core-cladding interface
must greater than critical angle (θ1 > θc)
iii. Incident angle at air-core interface must
smaller than acceptance angle (θi < θa) to
get θ1 > θc
θi < θa
In order for TIR to occur, ncore must be larger
than nclad . The greater their difference, the
larger the NA and maximum acceptance
angle, θa
Therefore for light could propagates inside the
fiber optic core in TIR manners, there are three (3)
conditions;

54
NUMERICAL APERTURE, NA
Numerical Aperture is the measure of the ability of an
optical fiber to capture the incident light ray inside it.
It measures the amount of light that can be accepted
by a fiber in order to get propagated.
A large NA implies that a fiber accepts a large amount
of light from the source.
𝐍𝐀 = 𝒏𝒄𝒐𝒓𝒆
𝟐 − 𝒏𝒄𝒍𝒂𝒅
𝟐
Above equation shows that NA depends upon the
refractive index, n of the core and cladding material and
does not depend on the physical dimension of the fiber.

55
NUMERICAL APERTURE, NA
To get higher NA, the difference between the two
refractive indices (ncore and nclad) must high.
The greater their difference, the larger the NA and the
maximum acceptance angle, θa.
NA also is defined as the maximum acceptance angle to allow and transmit light by an optical
fiber.
𝐍𝐀 = sin 𝜃𝑎
NA provides a good estimate of the maximum acceptance angle for most multimode
fibers. For a single mode fiber, NA is not a particularly required.
The number of modes that can be travelled though a multimode fiber are determined by core
diameter and NA. As the core size and NA increase, the number of modes increases.

QUESTION 9
In signal transmission system using fiber optics, there are two types of cable used which
are single mode and multimode. The light travels in multimode fiber optic from air into
fiber core with the speed at the core of 2.00 x 108 m/s and the speed of light at cladding
is 2.10 x 108 m/s while the incidence angle at core-cladding is 70°.The velocity of light in
air is 2.998 x 108 m/s. Calculate:
i. The index of refraction for core and cladding.
ii. Refraction angle of fiber at core-cladding
iii. Critical angle at the core-cladding interface
iv. Numerical aperture (NA)
v. Will this ray propagate down the fiber?
Justify the reason to support your answer.
56
EXERCISE
θr
θ1
air, n0
θi

i. The index of refraction for core and cladding.
57
EXERCISE
QUESTION 9 - SOLUTION
𝒄𝒐𝒓𝒆, 𝒏𝟏 =
𝒄
𝒗𝟏
=
𝟑 × 𝟏𝟎𝟖
𝟐 × 𝟏𝟎𝟖
= 𝟏. 𝟓
𝒄𝒍𝒂𝒅𝒅𝒊𝒏𝒈, 𝒏𝟐 =
𝒄
𝒗𝟏
=
𝟑 × 𝟏𝟎𝟖
𝟐. 𝟏 × 𝟏𝟎𝟖
= 𝟏. 𝟒𝟐𝟖
ii. Refraction angle of fiber at core-cladding
𝒏𝟏 𝐬𝐢𝐧 𝜽𝟏 = 𝒏𝟐 𝐬𝐢𝐧 𝜽𝟐
𝟏. 𝟓 𝐬𝐢𝐧 𝟕𝟎° = 𝟏. 𝟒𝟐𝟖 𝐬𝐢𝐧 𝜽𝟐
𝐬𝐢𝐧 𝜽𝟐 =
𝟏. 𝟓 𝐬𝐢𝐧 𝟕𝟎°
𝟏. 𝟒𝟐𝟖
𝜽𝟐 = sin−𝟏
𝟏. 𝟓 𝐬𝐢𝐧 𝟕𝟎°
𝟏. 𝟒𝟐𝟖
= 𝟖𝟎. 𝟕𝟖°
iii. Critical angle at the core-cladding interface
𝜽𝒄 = sin−𝟏
𝒏𝟐
𝒏𝟏
= sin−𝟏
𝟏. 𝟒𝟐𝟖
𝟏. 𝟓
= 𝟕𝟐. 𝟏𝟖°
𝑵𝑨 = 𝒏𝟏
𝟐 − 𝒏𝟐
𝟐
𝑵𝑨 = (𝟏. 𝟓)𝟐−(𝟏. 𝟒𝟐𝟖)𝟐= 𝟎. 𝟒𝟓𝟗
v. Will this ray propagate down the fiber?
NO. The light ray DO NOT propagate down the fiber because
incident angle, θ1 at core-cladding interface must be greater
than critical angle θc in order the light propagate down in the
fiber. However θ1= 70° < θc = 72.18°; therefore, total internal
reflection was NOT occur.

QUESTION 10
In signal transmission system using fiber optics, there are two types of cable used which
are single mode and multimode. If a light ray travels in a single mode optical fiber at the
incident angle of 35° at air-core, the index of refraction of core and cladding are 1.46
and 1.24 respectively, calculate
i. Refraction angle of fiber at air-core
ii. Critical angle at the core-cladding
iii. Incident angle at core-cladding
v. Acceptance angle
vi. Will this ray propagate down the fiber?
Justify the reason to support your answer.
58
EXERCISE
θr
θ1
air, n0
θi

59
EXERCISE
QUESTION 10 - SOLUTION
i. Refraction angle of fiber at air-core
𝒏𝟎 𝐬𝐢𝐧 𝜽𝒊 = 𝒏𝟏 𝐬𝐢𝐧 𝜽𝒓
𝟏. 𝟎 𝐬𝐢𝐧 𝟑𝟓° = 𝟏. 𝟒𝟔 𝐬𝐢𝐧 𝜽𝒓
𝐬𝐢𝐧 𝜽𝒓 =
𝟏. 𝟎 𝐬𝐢𝐧 𝟑𝟓°
𝟏. 𝟒𝟔
𝜽𝒓 = sin−𝟏
𝟏. 𝟎 𝐬𝐢𝐧 𝟑𝟓°
𝟏. 𝟒𝟔
= 𝟐𝟑. 𝟏𝟑°
ii. Critical angle at the core-cladding
𝜽𝒄 = sin−𝟏
𝒏𝟐
𝒏𝟏
= sin−𝟏
𝟏. 𝟐𝟒
𝟏. 𝟒𝟔
= 𝟓𝟖. 𝟏𝟒°
𝑵𝑨 = 𝒏𝟏
𝟐 − 𝒏𝟐
𝟐
𝑵𝑨 = (𝟏. 𝟒𝟔)𝟐−(𝟏. 𝟐𝟒)𝟐= 𝟎. 𝟕𝟕𝟏
vi. Will this ray propagate down the fiber?
YES. The light ray CAN propagate down the fiber because
incident angle, θi at air-core interface must be lower than
acceptance angle θa in order the light propagate down in
the fiber. Since θi= 35° < θa = 50.44°, therefore θ1 > θc,
then internal reflection will occur.
v. Acceptance angle
𝜽𝒂 = sin−𝟏 𝑵𝑨 = sin−𝟏 𝟎. 𝟕𝟕𝟏 = 𝟓𝟎. 𝟒𝟒°
iii. Incident angle at the core-cladding
𝜽𝟏 = 𝟗𝟎° − 𝜽𝒓 = 𝟔𝟔. 𝟖𝟕°

61
CONSTRUCTION OF FIBER OPTIC CABLE

62
CONSTRUCTION OF FIBER OPTIC CABLE
◼ Core - consists a fiber made of glass or plastic or any transparent material. The core is a path for
light propagation. Core is designed to have higher refractive index than cladding.
◼ Cladding – an insulator made of a glass or plastic or any transparent material that has optical
properties different from the core. It surround core to traps the light in the core using TIR.
◼ Buffer Coating - a non-transparent material which acts as a layer to protect the core and cladding
from damage.
◼ Strength members - surrounding the buffer, preventing stretch problems when the fiber cable is
being pulled. The materials can range from Kevlar to wire strands to gel-filled sleeves.
◼ Jacket - a layer to protect the fibre against abrasion, solvents, moisture, crushing and other
environmental dangers.

63
IMPORTANCE OF CLADDING IN LIGHT PROPAGATION
Cladding is a transparent material that has lower refractive index, n than core layer. The cladding
causes light to be confined in the core of the fiber by total internal reflection (TIR) at the boundary.
Light propagation : Bending of light ray

64
DIAMETER OF CORE AND CLADDING

65
Plastic Optical Fiber (POF) - is large core (about 1mm) fiber, usually for step index multimode
fiber which is used for short, low speed networks.
PCS/HCS – Plastic-clad silica (PCS) or Hard-clad silica (HCS) has a smaller glass core
(around 200 microns) and a thin plastic cladding.
DIAMETER OF CORE AND CLADDING

66
PROPAGATION MODE & INDEX PROFILE
Mode = path of light propagation
Index = refractive index, n

67
Figure 2.5

68
INDEX PROFILE
STEP INDEX PROFILE GRADED INDEX PROFILE
▪ the core has one uniformly-distributed
refractive index, n and
▪ Cladding has much lower refractive index than
core; causes the refractive index profile abruptly
changes at junction of core and cladding.
▪ Because of that, the light rays bend at difference
path length and travel asynchronized.
▪ the core has multiple gradually-distributed
refractive index, n
▪ the refractive index is highest at center of core and
decrease gradually until it reaching core-cladding
interface.
▪ Because of that, the light rays bend inward follow
sinusoidal paths and allows them to travel faster at
the lower refractive index region.

• Has smallest diameter of core compare to multimode
• Has only one path (mode) of light to propagate (also called “Lowest Order Mode”).
• Because of this, the number of light reflections created as the light passes through the core decreases
(low attenuation).
• Because of low attenuation, it creates the ability for the signal to travel further (suitable long distance
transmission).
• Application: usually used in long distance (about more than 5 km length), higher bandwidth runs by
Telco's, CATV companies, and Colleges and Universities.
• Higher transmission rate.
69
SINGLE MODE (SMF)

• Has multiple path (mode) of light to propagate.
• Has big diameter of core (common diameters in 50-to-100 µm range and the most common size is
62.5 µm).
• It is made of glass fibers. POF is a newer plastic-based cable which promises performance similar to
glass cable on very short runs, but at a lower cost.
• Has high bandwidth at high speeds over medium distances.
• However, in long cable runs (greater than 3000 feet), multiple paths (modes) of light can cause signal
distortion at the receiving end, resulting in an unclear and incomplete data transmission (not suitable
for long distance transmission).
70
MULTI MODE (MMF)

• Step Index Multimode
o high attenuation
o high dispersion
o too slow for many uses, due to the dispersion caused
by different path lengths of the various modes
travelling in the core.
• Graded Index Multimode
o use variations in the composition of glass in the core
to compensate the different path lengths of the
modes.
o It offers hundreds of times more bandwidth than
step index fiber - up to about 2 GHz
71
MULTI MODE (MMF)
▪ Two types are in used, 50/125 and
62.5/125.
▪ Where the numbers represent the
core/cladding diameter in micron (µ)
▪ 62.5/125 fiber has a 62.5 micron core
and a 125 micron cladding. It's now
called OM1 standard fiber.
▪ 50/125 fiber has a 50 micron core and
a 125 micron cladding and called OM2
standard fiber.
▪ Transmit data using LED.
▪ Wavelength range = 850 to 1300 nm.
Multimode Graded Index

SINGLE MODE MULTIMODE STEP INDEX MULTIMODE GRADED INDEX
- Small diameter of core (7 - 10µm) - Big diameter of core (50µm - 100µm) - Modest diameter of core (50µm - 85µm)
- The fastest transfer rate - Slower transfer rate - Modest transfer rate
- Low attenuation - High attenuation - Modest attenuation
- No modal dispersion - High modal dispersion - Low modal dispersion
- Suitable for long distance
transmission
- For short distance (high attenuation) - For modest distance
- Very expensive because hard to
build and very difficult to work with.
- Cheapest because easy to build - Cheaper
72
INDX PROFILE

QUESTION 11
Differentiate between a single mode, multimode step index and
multimode graded index in terms of propagation.
73
EXERCISE

1. Loose tube fiber cable
2. Tight-buffer fiber cable
3. Slotted Ribbon fiber cable
4. Armored fiber cable
74
TYPES OF FIBER OPTIC CABLE
There are four (4) types of fiber cable;
Zipcord Distribution Loose Tube Breakout
cable cable cable cable

75
1. LOOSE TUBE FIBER CABLE
• Composed of several fibers inside a small loose plastic tube, which are in turn wound around a
central strength member and jacketed, providing a small, high fiber count cable.
• The loose tube is filled with gel or water absorbent powder to prevent harm to the fibers from
water.
• Ideal for outside plant trucking applications.
• Some outdoor cables may have double jackets with a metallic armor between them to protect
from chewing by rodents or have a Kevlar for strength to allow pulling by the jackets.

76
2. TIGHT BUFFERED FIBER CABLE
• A tight-buffered cable design is better when cable flexibility and ease of termination are a
priority.
• Most indoor cables are of the tight-buffered design because of the relatively short
distances between devices and distribution racks.
• Military tactical ground support cables also use a tight-buffered design because of the high
degree of flexibility required.

77
2. TIGHT BUFFERED FIBER CABLE
• A tight-buffered fiber can be cabled with other fibers, and then reinforced with Aramid
yarn/Kevlar and jacketed to form a tight-pack distribution cable.
• Another option is to individually reinforce each fiber with Kevlar, then jacket it.
• Several single fiber units can then be cabled together to obtain a breakout-style cable where
each fiber can be broken out of the bundle and connectorized as an individual cable.
(Aramid yarn)

78
TIGHT BUFFERED vs LOOSE TUBE
loose tube fiber

79
Tight-Buffered Cable Loose-Tube Gel-Filled Cable
One fiber per buffer coating — excellent
mechanical and environmental protection.
Multiple fibers per loose tube.
No gel filling needed — exceptional tight-
buffered cable construction and aramid
strength members provide excellent
protection for every inch of the cable
Gel filling needed to prevent moisture
collection in tubes
No cleaning needed — no gel, easy to
handle, install and terminate, saving time
and costs, and improving reliability
Gel filling must be chemically cleaned —
messy, costly and time consuming
No stiff strength member needed, more
flexible cable — easier to handle
Requires stiff cable strength member —
more difficult to handle and install
Cable is "tight bound" and can be pulled
around multiple bends or hung vertically
(no fiber axial migration)
Should not be pulled around multiple
bends or hung vertically (fiber axial
migration) — installation limitations
Easy to terminate, no breakout kits or
splicing required.
Difficult to terminate, breakout kits or
splicing required — time consuming,
requires expensive equipment and skills
Lower total installed costs.
Cable purchase cost may be slightly
lower.

80
3. SLOTTED RIBBON FIBER CABLE
• This cable offers the highest packing density, since all the fibers are laid out in rows,
typically of 12 fibers, and laid on top of each other.
• Since it's outside plant cable, it's gel-filled for water blocking.

81
RIPCORD

82

83

84
Core Design 6 slots 6 slots
Ribbon Size 4 fibers/ribbon 8 fibers/ribbon
Fiber Count Up to 96 cores Up to 192 cores
One Slot
4 fiber x 4 tape = 16 fibers
16 fibers x 6 slots = 96 cores
Tape A
Tape B
Tape C
Tape D

85
4. ARMORED FIBER CABLE
• This cable have metal armoring between two jackets to prevent rodent penetration.
• Cables are installed by direct burial in areas where rodents are a problem.
• The cable is conductive (because have metal armoring). Thus, it must be grounded properly
Metal armored

86
4. ARMORED FIBER CABLE

88
OPTICAL LOSS / ATTENUATION
• Loss or Attenuation is measured in decibels (dB) unit.
• There are two (2) types of Optical Loss in fiber optic system;
i. Transmission Loss (Fiber Attenuation) – loss due to absorption,
scattering and radiation/bending. Normally measured per unit
length (in dB/km).
ii. Insertion Loss (Component Attenuation) – loss due to
splitters/couplers, WDMs, connectors, mechanical and fusion
splices, etc. Measured (in dB loss).

89
Loss in ‘FO’
Transmission Loss
Absorption Loss Intrinsic
Extrinsic
Scattering Loss
Radiation Loss
Macro-bending
Micro-bending
Dispersion Loss Modal
Chromatic
Polarization Mode
Insertion Loss
Coupling Loss
Splicing Loss
Connector Loss
Fiber
attenuation

90
TX RX
Medium and Devices
O
A
O
A
INSERTION LOSS
INSERTION LOSS
FIBER TRANSMISSION LOSS
-simple link : point to point link-

91
TRANSMISSION LOSS
• Definition: Transmission Loss or Fiber Attenuation is the reduction of intensity
(amplitude) of light beam signal with respect to the distance travelled through the
fiber optic cable.
• Transmission loss limits how far a signal can propagate in the fiber before the
optical power becomes too weak to be detected.
• It measures the amount of power loss between input and output and measured as
“the ratio of optical input power to the optical output power”
𝑨 𝒅𝑩 = −𝟏𝟎𝒍𝒐𝒈
𝑷𝒐𝒖𝒕
𝑷𝒊𝒏
𝑨 𝒅𝑩/𝒌𝒎 = −
𝟏𝟎
𝑳
𝒍𝒐𝒈
𝑷𝒐𝒖𝒕
𝑷𝒊𝒏
L = fiber length in km
dB formula;
dBW = 10 log (Power level /1W)
dBm = 10 log (Power level /1mW) DEP40053_Hanisah/JKE/PTSS

92
1. ABSORPTION LOSS
• Absorption Loss: An attenuation resulting from the conversion of optical power
into another energy form such as heat, caused by defect in fiber optic material.
• Absorption Loss occurs when photons interact with the atomic structure of glass,
electrons or metal ions in the fiber, causing the light power to be absorbed and
converted into other forms of energy, such as heat.
• Absorption can be limited by controlling the amount of impurities during the
manufacturing process.
• There are two types of absorption loss that is :
i. Intrinsic
ii. Extrinsic

93
1. ABSORPTION LOSS
i. INTRINSIC ABSORPTION
• Intrinsic Absorption is an attenuation caused by defect of fiber-material properties
itself.
• Intrinsic Absorption occurs as a result of the inherent interaction between;
i. photons (light particles) and glass silica structure of fiber which results in dissipation
of some of the transmitted optical power into heat. – Material Absorption
ii. photons and electrons which causes electrons to be excited to a higher energy level.
– Electron Absorption.
• Glass fibers have low absorption than plastic fibers, thus it is preferred for long haul
communications.
• To minimize intrinsic absorption;
✓ use ultra-pure glass and dopant chemicals to minimize fiber-impurities
✓ having clean fiber

94
1. ABSORPTION LOSS

95
1. ABSORPTION LOSS
ii. EXTRINSIC ABSORPTION
• Extrinsic Absorption is an attenuation loss where the light signal power is absorbed by
natural impurities inside glass fiber.
• Extrinsic Absorption is caused by unwanted particles or impurities such as iron, nickel,
chromium optical fibers, that are present during the manufacturing process of fiber
optic cables.
• It is also call fiber contamination.
• Also occurs when hydroxyl ions (OH), due to presence of water vapor are introduced
into the fiber.
• To minimize extrinsic absorption;
✓ use glass refining techniques such as vapor-phase oxidation during the process of
fiber manufacturing which largely eliminates the effects of these metallic impurities.

96
2. SCATTERING LOSS
• Scattering : a diffusion of a light beam caused by microscopic variations in the material
density of the transmission medium.
• Scattering is caused by the interaction of light with density fluctuation within a fiber.
• Density fluctuation is caused by the contamination of unwanted materials such as dust
and air bubbles inside fibers during fiber manufacturing.
• Scattering also called Diffuse reflection.
• This material scattering (also called Rayleigh scattering) will scatters light out of the
core.

97
2. SCATTERING LOSS
• Rayleigh scattering causes 96% of attenuation in optical fiber.
• “As wavelength increase, Rayleigh Scattering decrease”
• Short wavelengths are scattered more than longer wavelengths.
• Any wavelength that is below than 800nm is unusable for optical communication due to
high Rayleigh scattering attenuation/loss.
• Material Scattering can be reduced by improvise the fiber fabrication/manufacturing.

98
2. SCATTERING LOSS

99
3. RADIATION LOSS
• Radiation loss: is a loss occurs at the bend of fiber optic cable.
• Also known as signal Bending Loss.
• There are two types of radiation loss;
i. Macrobending Loss - curvature radius of the bend is much larger than the diameter
of the fiber.
ii. Microbending Loss - small-scale bends in the core-cladding interface.
• Bends can cause the change of incident angle of light ray at core-cladding boundary
that resulting in the light ray escape into cladding.
Microbending Loss Macrobending Loss

100
i. MACROBENDING LOSS
• Macrobending Loss: is a radiation loss due to the fiber is bent into a larger radius of
curvature than fiber diameter (large bends)
3. RADIATION LOSS
• If the radius of the core is large compared to fiber diameter, it may cause large-curvature at the
corner.
• At this corner the light will not satisfy the condition for TIR and hence it escapes out from fiber.
• Macrobend may be found in a splice tray or a fiber cable that has been bent.
• Macrobend won’t cause significant radiation loss if it has small bending.
Escaping Rays
Escaping Rays
45°

101
ii. MICROBENDING LOSS
• Microbending Loss: is a radiation loss due to non-uniformities or micro bends at core-
cladding interface.
3. RADIATION LOSS
• These micro bends in fiber appears due to;
✓ non-uniform pressures during the manufacturing
✓ Improper cabling jacket surrounding the fiber and uneven coating applications
✓ non-uniform pressure during wrapping the fiber on a spool or bobbin
• This lead to loss of light by leakage through the fiber.
Escaping Rays
Micro bends

102
4. DISPERSION LOSS
• Dispersion: spreading (broadening) of the optical pulses as it travels along the fiber.
• Also known as signal Distortion.
• Dispersion occurs due to different travelling speeds or different arrival times of input
light pulses.
• If the signal pulse rate is too fast, dispersion will cause the pulses to overlap giving rise
to distortion (deterioration of optical signal).
(Broadened pulses)

103
4. DISPERSION LOSS
• Effect of dispersion in data transmission;
i. Dispersion corrupts the transmitted signal – broadened pulses (overlap pulses)
cause the information mixing between pulses and actual information will not be
obtained at receiver end.
ii. Limits the information carrying capacity – broadened pulses limit the number of
pulses transmitted (data rate), then information carrying capacity of signal gets
reduced.
• Two main factors which cause dispersion are different sources of modes (paths) and
wavelengths.
• To reduce dispersion distortion, the number of modes the fiber supports must be
reduced. This is achieved by reducing the diameter of the core.

104
4. DISPERSION LOSS
• There are three (3) types of dispersion;
i. Modal Dispersion / Intermodal Dispersion – MMF
ii. Chromatic Dispersion / Intramodal Dispersion – SSF & MMF
iii. Polarization Mode Dispersion (PMD) – SMF

105
i. MODAL DISPERSION
• Modal Dispersion: is a distortion of optical pulses because of different modes (paths)
of light rays take different times to arrive.
4. DISPERSION LOSS
Original pulse
• Modal dispersion occurs when the rays travel along multiple paths have multiple path
lengths and speeds.
• Since the rays do not travel the same distance, different rays will arrive at the end of
the fiber at different times and causes the output pulses signal distorted (overlap).
High dispersion Low dispersion

106
4. DISPERSION LOSS
i. MODAL DISPERSION
• Only happens in multimode fiber (MMF) ; limits its performance.
• As length fiber increase, modal dispersion increase.
• Can be reduced by using graded-index fiber or reduce the diameter of core.
Different paths

107
ii. CHROMATIC DISPERSION
• Chromatic Dispersion: is a distortion of optical pulses because of differential arrival
time of the different colors(wavelengths) of input lights due to different speeds.
4. DISPERSION LOSS
• Also known as Material Dispersion, Spectral Dispersion or Intramodal Dispersion.
• Chromatic dispersion occurs when white light is used instead of monochromatic light.
Therefore, larger effect with LED than LASER (laser produce monochromatic light).
Chromatic dispersion
Original pulse

108
4. DISPERSION LOSS
• As we know a white light ray is composed of components of a different wavelengths(colors).
• Different wavelengths of light have different speeds when travel inside medium others than vacuum.
• Due to different speeds (v) of light, the refractive Index (n) of the SAME material is also varied. “As
the wavelength decrease, the speed will decrease and the refractive index of material increase
and vice-versa”
• Since different wavelengths (colors) of light travel at different speeds with different refractive index,
they will bend at different angles of refraction.
• Blue light travels slower than red light due to the greater refractive index. Therefore, the red light
reaches the end before the blue light.
Original pulse Chromatic dispersion

109
4. DISPERSION LOSS
• Occurs in both single mode (SMF) and multimode fiber (MMF)
• Chromatic dispersion is less pulse broadening and has far smaller effect than modal
dispersion.
• Can be reduced by using monochromatic light.

110
4. DISPERSION LOSS
Effect of chromatic dispersion is somewhat smaller as
compared to modal dispersion.

111
iii. POLARIZATION MODE DISPERSION (PMD)
• PMD : is a distortion of optical pulses because of differential arrival time of the different
polarization modes/states of input lights due to different speeds.
4. DISPERSION LOSS
• PMD is only important in single mode fibers (SSF). In SSF, only one mode (path) of light
pulse can propagate.

112
4. DISPERSION LOSS
• Light pulse is an electromagnetic wave that consist two orthogonal polarization states
of an electric field E.
One pulse = Two orthogonal polarization states
The electric field E is decomposed into two polarization
states (fast and slow)
• Single-mode fiber supports one propagation mode(path) which is composed of two
orthogonal polarization states.

113
4. DISPERSION LOSS
• If light pulses travel through a perfectly cylindrical optical fiber, both polarization states would
travel at exactly the same speed.
• However, in the real world there are stresses and manufacturing flaws in the optical fiber
causing it to be non-cylindrical.
• These asymmetrical variations introduce small refractive index variations between the two
polarization states.
• This causes one polarization state to travel faster than the other, resulting in a distorted signal
at the output of the fiber.
Delay
Broadened (distort) pulses

114
4. DISPERSION LOSS

115
END OF CHAPTER..

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