This document provides an overview of optical fibers, including their definition, main components, types, parameters, transmission properties, attenuation factors, dispersion effects, and applications. Optical fibers are thin strands of glass that transmit light signals over long distances using total internal reflection. They have a higher glass core surrounded by a lower index cladding. Key fiber types are single-mode and multimode (step-index and graded-index), which differ in core size and number of propagation modes. Parameters like acceptance angle, numerical aperture, and normalized frequency determine fiber properties and performance.

1. Optical Fibers

2. Topics:
• Introduction
• Definition
• Parts of Optical Fibre
• Types
 Step Index
 Graded Index Fibres
• Parameters of Optical Fibres
 Acceptance Angle
 Acceptance Cone
 Numerical Aperture (NA)

3. Cont…….
Topics:
• Normalized Frequency
• Number of Modes
• Attenuation in Optical Fibres
• Dispersion
1. Intermodal Dispersion
2. Intramodal Dispersion
• Applications
1. Optical fibres in Communication
2. Sensors

4. Introduction:
• Optical fibers are
long, thin strands of
very pure glass
usually 125 µm in
diameter. They are
arranged in bundles
called optical cables
and used to transmit
light signals over long
distances.

5. What is optical fiber
• Optical fibers are very fine fibers of glass. They consist of
a glass core, roughly fifty micrometres in diameter,
surrounded by a glass "optical cladding" giving an
outside diameter of about 125 micrometres. They make
use of total internal reflection to confine light within the
core of the fiber.

6. Parts of Optical Fiber
• Core – thin glass center of the fiber where
light travels.
• Cladding – outer optical material
surrounding the core.
• Buffer Coating – plastic
coating that protects
the fiber.

7. Optical Fiber

8. Transmission of Light Through Optical
Fibers
• Total Internal Reflection

9. Reflection & refraction
μ2< μ 1 2 μ 2< μ 1 μ 2< μ 1
2
1 1 1= c
1> c
μ1 1 μ1 c μ1
Snell’s law Critical angle Total internal
reflection
2
sin c
1

10. Total Internal Reflection
• The angle of the
light is always
greater than the
critical angle.
• Cladding does not
absorb any light
from the core.
• The extent that the
signal degrades
depends upon the
purity of the glass
and the wavelength
of the transmitted
light.

11. Fiber Technology

12. THE OPTICAL FIBER
CLADDING
AIR or JACKET (Lower index)
Dia ~ 125 µm
CORE
(Higher index)
Dia ~ 5 – 50 µm
μclad
μcore
μclad

13. PROPAGATION THROUGH
AN OPTICAL FIBER
fast
input output
t fast slow
t

14. Types of optical fibres
Based on their transmission properties and the
structure they are of two types
1. Single Mode Fibre
2. Multimode Fibre
(a) Step Index Fibres
(b) Graded Index Fibres

15. Single (Mono) Mode :
This is called so because the refractive index of the fibre ‘step’
up as we move from the cladding to the core and this type of
fibre allows single mode to propagate at a time due to very
small diameter of its core.
μ clad
μcore
μ clad
 In this fibre, the refractive indices of the
cladding and the core remain constant
 In this fibre, the size of its core
(diameter) is typically around 9-10
μm.

16. Multimode fibre :
This is called so because it allow more than one mode to
propagate. Over more than 100 modes can propagate
through multimode fibres at a time. The size of its core is
typically around 50 μm or 62.5 μm.
Two Types
 Step Index Fibres
 Graded Index Fibres

17. Multimode Step Index Fibres:
No of propagating modes α Core diameter/ Wavelength
Typically the core diameter is 50 μm to 100 μm and Numerical
Aperture (NA) varies from 0.20 to 0.29 respectively
Due to higher value of NA , and larger core size in this case,
fibre connections and launching of light is very easy
Due to several modes, the effect of dispersion gets increased,
i.e. the modes arrive at the fibre end slightly different times
and so spreading of pulses takes place.
μclad
μ core
μ clad

18. Multimode Graded Index Fibres:
In this fibre, the refractive index of the core decreases with
increasing radial distance from the fibre axis.
The value of the refractive index is highest at the centre of the
core and decreases to a value at the edge of the core that
equal the refractive index of the cladding.
μclad
μcore
μclad
By this type of fibre design, the dispersion of the modes is
compensated. Also, light wave follow sinusoidal paths along
the fibre.

19. The profile of the refractive index is nearly parabolic that
results in continual refocusing of the ray in the core, and
minimizing the model dispersion.
Standard graded index fibres typically have a core diameter of
50 μm or 62.5 μm and the cladding diameter of 125 μm.
Advantage of Graded Index Fibre over Step Index Fibre
Decrease in the modal dispersion

20. Advantage of Single Mode Fibre over Multi Mode Fibre
Lower signal loss and a higher information capacity or
bandwidth than multimode fibres as the signal loss
depends on the operational wavelength.
These fibres are capable of transferring higher amount of
data due to low fibre dispersion.
 Single mode fibres are known as low loss fibres

21. Comparison

22. Fiber types Cont…….
SM
Single-Mode
MM-SI
Multi-Mode
Step Index
MM-GI
Multi-Mode
Graded Index
refractive
index

23. Cont…….
singlemode multimode
Types of Fibers
step-index step-index
μclad
μcore
μclad
μclad
μcore
μclad
μclad
GRIN
μcore
μclad

24. Fiber Types Cont……
© 2006, VDV Works LLC

25. PROPAGATION THROUGH
AN OPTICAL FIBER
By grading the index profile in the core, the pulse
broadening was reduced, but it was suggested in 1980 that
one could make single-mode fibers which will allow only
“one path” through the fiber, thereby removing the pulse
broadening
input output
t t
μclad
μcore
μclad

26. GRADIENT-INDEX OPTICAL FIBER
μclad
μcore
μclad
input output
t fast slow
t
Longer path is now located in lower index region; the larger time taken
is compensated by faster travel leading to less pulse broadening

27. Acceptance angle
• acceptance angle: In fiber optics, half the vertex angle of that
cone within which optical power may be coupled into bound
modes of an optical fiber.
• Note 1: The axis of the cone is collinear with the fiber axis, the
vertex of the cone is on the fiber end-face, and the base of the
cone faces the optical power source.
• Note 2: The acceptance angle is measured with respect to the
fiber axis.
• Note 3: Rays entering an optical fiber at angles greater than the
acceptance angle are coupled into unbound modes.

28. Acceptance angle Cont………
Multimode fiber
n0
n0 μ2
0 μ1
c
2
Critical angle: sin c
1

29. Numerical Aperture
Multimode fiber
μ0
n0 μ2
0 μ1
c
Numerical aperture:
2 2
NA 0 sin 0 sin 0 1 2 for 0 1
if 1 2 :
2 2 2 2
1 2 1 2 NA 1 2 2 2
2
2 1 1
Here Δ is the relative refractive index difference NA 0.1 0 , max 6
Or fractional refractive index

30. Acceptance Cone
Ls
Acceptance A B
Cone
o θr d
θr
θ0
The cone
associated with
Acceptance angle θ0:
the angle 2θ0 is 2 2
sin 0 1 2
called the
acceptance cone 0 sin 1
1
2
2
2

31. Parameters of Optical fibres
2 2
sin
Acceptance angle = 0 1 2
1 2 2
0 sin 1 2
Acceptance Cone = 2θ0
2 2
Numerical Aperture (NA) = Sinθ0 = 1 2
2
Skip Distance Ls= d 1
1
0 sin i
1
2
Number of reflections Nr = 1
d 1
0 sin i

32. Numerical Problems
Activity 1: The refractive indices for core and cladding for a
step index fibre are 1.52 and 1.41 respectively
Caculate (1) Critical angle (2) Numerical Aperture
(3) The maximum incidence angle
Hints: Given Here =μ1 = μcore = 1.52, and μ2 = μclad = 1.41
Ans = 68.060
Critical angle θc = sin-1 (μ2/ μ1)
2 2 Ans = 0.568
Numerical Aperture 1 2
2 2
Maximum incidence angle (θ0)= sin 1
1 2
Ans θ0 = 34.60

33. Numerical Problems
Activity 2: A light ray enters from air to a fibre. The refractive
Index of air is 1.0. The fibre has refractive index of core is
equal to 1.5 and that of cladding is 1.48. Find the critical
Angle, the fractional refractive index, the acceptance angle and
Numerical aperture.
Hints: Given Here =μ0 = μair = 1.0; μ1 = μcore = 1.5, and μ2 = μclad
= 1.48
Critical angle θc = sin-1 (μ2/ μ1) Ans: θc = 80.630
1 2
Fractional Refractive index = 1.33% of light
1
Ans = 0.568
2 2
Numerical Aperture 1 2
1 2 2
Acceptance angle (θ0) = sin 1 2 Ans θ0 = 14.130

34. Numerical Problems
Activity 3: Calculate the refractive indices of the core and
cladding material of fibre from the following data:
NA = 0.22, Δμr = 0.012 and
core cladding
r
core
Hints:
Fractional Refractive index 1 2
1
Numerical Aperture 2 2
1 2
Ans : μ1= 1.424 = μcore and μ2= 0.988 μ1 = 1.41 = μcladding

35. Allowed Modes and Normalized Frequency
2
Maximum Number of modes that 1 d
propagate successively in the fibre mm NA
2
d
mm
Hence, number of possible modes will be larger for higher ratio d/λ
For multimode fibres mm > 2 OR
d 2
For single mode fibres mm < 2 NA
As is evident the parameter mm decides the number of possible
modes since this parameter depends on core diameter d and
the numerical aperture NA. Therefore, the number of allowed
modes would be different for fibres of different core diameters.

36. V number: determines how many modes a fiber
supports
2 d 2 d
V-parameter V 1
2
2
2
NA
Single-mode fiber: V 2.405
Normalized d d 2 2
Frequency n NA 1 2
Therefore, the number of modes mm in terms of
normalized frequency is
2
n 2 a 2 2 2 a
mm V n1 n2 NA
2

37. Numerical Problems
Activity 4: An optical fibre operating at 1.50 μm has a small
Value of core diameter 5.0 μm and fractional refractive index
difference of 0.0075. Calculate the normalized frequency
and acceptance angle, given μ2 = 1.4.

38. Cut-off Wavelength
Definition: the wavelength below which multiple
modes of light can be propagated along a particular
fiber, i.e., λ> = λ c, single mode, λ < λc, multi-mode
2 d
c NA
2.405

39. Attenuation in optical Fiber
• When light travels along the fibre, there is a loss of
optical power, which is called attenuation.
Definition:
Attenuation: Ratio of optical input power (Pi) to the
optical output power (Po)
Optical Input power: The power transmitted into the fibre
from an optical source
Optical output power: The power received at the fibre end

40. Fiber Attenuation Cont……..
This relation defines the signal attenuation or absorption
coefficient in terms of length L of the fibre:
10 P
log 10 i
L P0
Length L of the fibre is expressed in kilometers
Here, the unit of Attenuation is decibels/kilometer i.e. dB/km.
The main causes of attenuation in optical fibre are:
(a)Absorption
(b)Scattering
(c)Bending losses
Each mechanism of loss is influenced by the properties of fibre
Material and fibre structure.

41. Fiber Attenuation Cont……..
Absorption losses over a length L of fiber can be described
by the usual exponential law for light intensity (or irradiance) I
L
I I 0e
Where I0 is the initial intensity or the irradiance of the light.

42. The attenuation profile is shown in figure which shows the amount of
Attenuation is also wavelength dependent.
In the figure, two
absorption peaks at
1.25 μm and 1.4 μm
are observed which are
respectively due to the
peculiarities of the
single mode fibre and
the traces of water
remaining in the fibre as
an impurity.
For commercially available fibers
Loss 0.5 dB/km @ 1310 nm
0.25 dB/km @ 1550 nm

43. Dispersion
• A pulse of light sent into a fibre broaden in time as it
propagate through the fibre. This phenomenon is
known as pulse dispersion.
• Intermodal Dispersion: Different rays take different
times to propagate through a given length of the fibre.
Or Different modes travel with different speeds
• Intarmodal dispersion: Any given source emits over a
range of wavelength and because of the intrinsic
property of the material of the fibre, different
wavelength takes different amount of time to
propagate along the same path.

44. Dispersion in Fiber Optics
• Dispersion occurs when photons from the same light
pulse take slight different paths along the optical fiber.
Because some paths will be longer or shorter than other
paths the photons will arrive at different times thus
smearing the shape of the pulse.
• Over long distances, one pulse may merge with another pulse.
When this happens, the receiving device will not be able to
distinguish between pulses.
The dispersive effects in a single mode fibre are much smaller than a
multimode fibre. Due to dispersion, optical pulses in optical fibres
spread and hence the signal spread over long distances.

45. Pulse Dispersion in Optical Fibre
In optics, dispersion is the phenomenon in which the
phase velocity of a wave depends on its frequency.
Such medium is called a dispersive medium.

46. Intermodal Dispersion
Different rays take
different times to
propagate through a given
length of the fibre.
In the language of wave
optics, this is known as
intermodal dispersion
because it arises due to
the different modes
travelling with different
speeds.

47. Intramodal Dispersion
Any given light source emits
over a range of wavelength
and because of the intrinsic
property of the material of the
fibre, different wavelengths
takes different amounts of
time to propagate along the
same path. This is known as
material dispersion or
intramodel dispersion

48. Cont……..
There are several factors that cause dispersion in
optical fibres.
For Example:
(1) In multimode fibres different axial speeds of different
transverse modes cause intermodal dispersion that limits
the performance of the fibre.
(2) In singe mode fibres, though intermodal dispersion
is eliminated, chromatic dispersion occures because of
The slight variation in the index of the glass with the
wavelength of the light.
Dispersion limits the bandwidth of the fibre because the
spreading optical pulses limit the rate that pulses can
follow one another on the fibre and still remain
distinguishable at the receiver.

49. Chromatic Dispersion
For example, when white light passes through a prism some of the
wavelengths of light bend more because their refractive index is
higher, i.e. they travel slower This is what gives us the "Spectrum" of
white light. The "red' and "orange" light travel slowest and so are bent
most while the "violet" and "blue" travel fastest and so are bent less. All
the other colours lie in between
Figure -The Dispersion of White Light

50. Massage Modulator Optical
Input (Transmitter) Source
Optical
Fibre Optics Communication Fibre
Demodulator Optical
Destination (Receiver) detector

51. A TYPICAL OPTICAL
COMMUNICATION SYSTEM
Electrical Signal Electrical Signal
Optical Fiber
Optical Source External
LED or Laser Modulator
Connector/
Optical
Splice
Optical Detector
PIN Diode Amplifier
Processing electronics

52. Optical Fibre Sensors
Optical Fibre sensors are fibre based devices that are used for
sensing some typical quantities like temperature of
mechanical strain.
These sensors are sometime used for sensing vibrations,
pressure, acceleration or concentrations of chemical species
Principle: When a light beam is sent through a optical fibre,
then its parameters either in the fibre or several fibre
Braggs grating experience subtle change. Then the light
reaches a detector arrangement measure these changes.
The light may be changed in five of its optical properties i.e.
intensity, phase, polarization, wavelength and spectral
distribution.

53. Optical Fibre Sensors
(A) Intrinsic Sensors (B) Extrinsic Sensors
(A) Intrinsic Sensors
Fibre
Pressure
Light A Light
Source B Detector
Pressure
•In this type of fibres, sensing medium is itself fibre
•Measure the variation in Intensity of transmitted light signals
•Useful in measuring the force being exerted between the two objects
•If one apply the pressure then due to micro bending losses the light
•intensity at the detector will decrease
•If we remove the pressure the intensity will increase.

54. (B) Extrinsic Sensors
•The delivery of light and its collection is done by the fibre
•Used to measure vibration, rotation, displacement, velocity,
acceleration, torque and twisting.
•A major benefit of these sensors is their ability to reach
places which are otherwise inaccessible .
FOR EXAMPLE:
Useful to measure the temperature inside aircraft jet engine.
Used to measure the internal temperature of electrical
transformer.

55. (B) Extrinsic Sensors Cont……..
Light Light
Source Detector
Feed Fibre l
Return Fibre
The amount of light launched into the return fibre will
decrease as the distance between the two fibers is
increased. However if length is decreased the light
intensity collected by the receiver will decrease. This
way these optical fibre sensors are capable of
determining small shifts between objects.

56. Advantages of optical fibres compared with
Traditional metal communication lines:
1. Fibre optics cables can carry more data as their bandwidth is
greater than metal cables
2. Fibre optics cables are less susceptible (sensitive) then metal cables
to interference.
3. Fibre optic cables are much thinner and lighter than metal wires.
4. Through fibre optic cables the data can be transmitted digitally rather
than analogically.
5. Attenuation through fibre cables is very low in transmitting the data
over a long distance, so there is no need of repeaters (thing that
repeats)

57. An optical fiber (or fibre) is a glass or plastic fiber that carries
light along its length.
Fiber optics
Applied science Engineering
Optical fibers are widely used as these
• permits transmission over longer distances
•and at higher bandwidths (data rates) than other forms of
communications.
•Fibers are used instead of metal wires because signals travel
along them with less loss, and they are also immune to
electromagnetic interference.

58. Areas of Applications
• Carry plain old telephone service (POTS)
• For transmission of data
• Transmitting broadband signals
• In the biomedical industry
• Non-Communication Applications (sensors etc…)
• Telecommunications
• Local Area Networks
• Cable TV
• Optical Fiber Sensors

59. The advantages of fiber optic over wire
cable
• Thinner
• Less Expensive
• Higher carrying capacity
• Digital signals
• Less signal degradation
• Light weight
• Light signal
• Non-flammable
• Low power
• Flexible

60. DISADVANTAGES OF OPTICAL FIBERS…
 The terminating equipment is still costly as compared to copper
equipment.
1. IT has to be handled carefully.
2. Optical fiber is more expensive per meter than copper
Communication is not totally in optical domain, so repeated
electric –optical – electrical conversion is needed.
1. Tapping is not possible. Specialized equipment is needed to tap a
fiber.
1. Optical fiber splicing (joining by interweaving strands) is a
specialized technique and needs expertly trained manpower.

61. DISADVANTAGES OF OPTICAL FIBERS…
1. The splicing (joining by interweaving strands) and testing
equipments are very expensive as compared to copper
equipments.
2. Optical fiber can not be join together as easily as copper cable. It
requires training and expensive splicing (joining by interweaving
strands) and measurement equipment.

62. A Light Sources
LED (Light emitting diode) ILD (injection laser diode)

63. Optical source
TRANSMITTER
FIBER
Performance
+ – Modulation speed
Fiber-coupled power

64. Light Emitting Diode (LED)
– +
Typical performance data
Power in MM-fiber: 100 W
Power in SM-fiber: 1 W
Direct Modulation Bandwidth: 100 MHz

65. Laser
Typical performance
Power (in fiber): 5-10 mW
Max: 100-300 mW
Direct Modulation Bandwidth: 1-10 GHz

66. • Telecommunications
• Internet Access
• Cable and Satellite
Television
• Decorative Light Source

67. Characteristics
• Glass Core
• Glass Cladding
• Ultra Pure Ultra Transparent Glass
• Made Of Silicon Dioxide
• Low Attenuation
• Popular among industries

68. Towers

69. Buildings

70. Towers

71. Installation of Antennas

72. Thank You

73. Any Questions or Comments?