Fiber optics uses total internal reflection to transmit light signals through thin glass or plastic fibers. It consists of a core surrounded by a cladding and a protective jacket. Light is confined to the core by total internal reflection at the core-cladding interface. Optical fibers have low attenuation and can transmit high bandwidth signals over long distances, making them useful for voice, television, and data communication.

1. Fiber Optics

2. Introduction
Optical fiber is a long thin transparent dielectric
material which carries EM waves of visible and IR
frequencies from one end to the other end of the
fiber by means of TIR.
NOTE: Glass or Plastic is used as Dielectric
material.
Optical fibers works as Wave guides in optical
television signals, digital data to transmit voice
television signals, digital data to any desired
distance from one end to the other end of the fiber.

3. Optical fiber consists of three sections
1. Core 2. Cladding 3. Protective Jacket
Core: It is an inner cylindrical material made up of glass or plastic.
Cladding: It is a cylindrical shell of glass or plastic material in which
Core is inserted.
Protective Jacket: The Cladding is enclosed in polyurethane jacket
and it protects the fiber from surroundings.
NOTE: The RI of core is slightly greater than the RI of Cladding. The
normal standard values are 1.48 and 1.46 respectively.

4. Structure of an Optical
fiber
Poly urethane protective jacket
Cladding
Core
• Principle: Optical fiber works on the principle of TIR. Once
light ray enters into core ,it propagates by means of multiple
TIR’ s at core-cladding interface.

5. 
c c 
DENSAR MEDIUM
RERAR MEDIUM
NORMAL

NORMAL
r r = 90

6. 
c 
NORMAL
RERAR MEDIUM
DENSAR MEDIUM

7. 1
2
0
1
2
0
21
sin
90sinsin
90
sinsin
n
n
n
n
r
rnn
refractionoflawtoaccording
c
c
c









8. Acceptance Angle
• The maximum angle of incidence at the end face of
an Optical fiber for which the light ray can be
propagated along Core-Cladding interface is known
as maximum Acceptance angle. It is also called
Acceptance cone half angle.

9. Core-Cladding interface
Fiber axis
Core n1
Cladding n2
A
B
C
θr
θi
θr
θ
Incident light ray

10. Applying Snell’ s law for Air-Core media
)2.........(cossin
cossin
)90sin(sin
90
90
)1....(..........sinsin
0
1
10
0
10
0
0
10






n
n
nn
nn
ABCtriangleanglerightthefrom
nn
i
i
i
r
r
ri







11. )4..(..........cos
)(1sin1cos
sin
90sinsin
90
sinsin
)3......(..........cossin
)(
1
2
2
2
1
2
1
22
1
2
0
1
2
0
21
0
1
n
nn
n
n
n
n
n
n
ri
rnin
refractionoflawtoaccording
n
n
anglecriticalwhen
c
cc
c
c
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cm
mic

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12. 2
2
2
1
1
max
2
2
2
1
0
1
2
2
2
1
0
1
sin
sin
1,
sin
)3()4(
nn
nn
nthenairisfiberthegsurroundinmediumtheif
n
nn
n
n
inequationsubstitute
m
m









Which is required expression for Maximum
Acceptance Angle in optical fibers.

13. Acceptance Cone
Rotating the Acceptance angle about the fiber axis
describes the Acceptance Cone of the fiber.
Light launched at the fiber end within this Acceptance
Cone alone will be accepted and propagated to the other
end of the fiber by total internal reflection.
θm
θm
Acceptance Cone

14. Numerical Aperture
• The light gathering capacity of an
optical fiber is known as Numerical
Aperture and it is proportional to
Acceptance Angle.
• It is numerically equal to sine of
minimum Acceptance Angle.











2
2
)(
))((
sin
sin
1
2
1
21
211
1
21
2121
2
2
2
1
0
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2
2
1
max
max
nNA
nNA
nn
nnnNA
n
nn
nnnnNA
nnNA
n
nn
NA


The ratio between the difference
in RI’s of
Core and Cladding to that of RI of
core is called the fractional change.

15. TYPES OF OPTICAL FIBRES
On the basis of variation of RI of core, the optical fibers
are mainly classified into following types. i.e.,
1.Step Index fiber 2.Gradex Index fiber
NOTE: Based on Mode of propagation, the fibers are
further divided into Single Mode and Multi Mode.

16. Single Mode Step Index fiber
The RI is constant for the core in this fiber. As we go radically from
center of the core, the RI undergoes a step change at core-cladding
interface .
The core diameter of this fiber is about 8 to 10µm and the outer diameter
of cladding is 60 to 70µm.
There is only one path for light ray propagation. Hence it is called single
mode step index fiber.
It is a reflective fiber since light is transmitted from one end to the other
end of a fiber by TIR.
These are extensively used because distortion and transmission losses are
very less.

17. Refractive index profile of
single mode step index fiber
Radial distance
60 to 70 µm
8 to 10 µm
RI

18. SINGLE MODE STEP INDEX FIBER
CORE
CLADDING
RAY
PROPAGATION

19. Multimode Step Index Fiber
The construction of this fiber is similar to Single mode
step index fiber but dimensions of Core and Cladding
are much larger to have more number of paths for
light propagation.
The Core diameter varies from 50 to 200µm and the
Cladding diameter varies from 100 to 250µm.
It is also a reflective fiber since light is propagated in
the form of multiple TIRS.

20. Radial distance
100 to 250 µm
50 to 200 µm
RI
REFRACTIVE INDEX PROFILE OF MULTI MODE STEP INDEX FIBRE

21. GRADED INDEX FIBRE
In this fiber , Radially the RI of Core continuously
decreases from center to the surface.
The RI is maximum at the center of Core and Minimum
at the Surface.
This fiber can be a single mode or Multimode ,the
diameters of core and cladding varies from 50-200µm and
100-250µm respectively.

22. Radial distnce
100 to 2500 µm
50 to 200 µm
RI
REFRACTIVE INDEX PROFILE OF SINGLE MODE GRADED INDEX FIBER

23. Radial distance
100 to 250 µm
50 to 200 µm
RI
REFRACTIVE INDEX PROFILE OF MULTIMODE GRADED INDEX FIBRE

24. • As RI changes continuously radially in Core, the light
rays suffers continuous refraction with in the Core from
its center to surface.
• Thus the propagation of light rays are not due to TIR
but by refraction. Therefore it is called Refractive fiber.
• In this fiber, the light rays travel at different speeds in
different parts.
• Near the surface RI is least so, the light rays travel
faster compared to the light rays near the axis. Because
of this all the rays almost arrive at the same time at the
other end of the fiber.

25. CLADDING
CORE
LIGHT PROPAGATION IN MUTI-MODE
GRADED INDEX FIBRE

26. Optical fiber Communication System
• An efficient optical fiber communication system
requires high information carrying capacity such
as voice signals, video signals over long
distances with a minimum number of repeaters.
It essentially consists of following parts.
1.Encoder 2. Transmitter 3.Wave guide
4.Receiver 5.Decoder

27. • 1.Encoder: It converts electric signal corresponding to
analog information such as voice, figures, objects etc
into a binary data. This binary data comes out in the form
of stream of electrical pulses.
• 2.TRANSMITTER: It mainly consists of drive circuit and
a light source. Drive circuit supplies the electric pulses to
the light source from the encoder.
• NOTE: LED or diode laser is used as light source and it
converts electrical signals are infected into optical
signals. These optical signals are injected into wave
guide.

28. Electrical
signal
ENCODER
DRIVE SOURCE LIGHT SOURCE
TRANSMITTER
OPTICAL SIGNAL
AMPLIFIER
PHOTO
DETECTOR
SIGNAL
RESTORER
DECODER
Wave guide
receiver

29. Attenuation or Power loss in Optical fibers
• The power of the light at the out put end is found to be
always less than the power launched at the input end.
• Attenuation is found t be a function of fiber material,
wavelength of light and length of the fiber and it is
measured in terms of the decibel.
Attenuation mainly three types….
1.Scattering losses
2.Absorption losses
3.Bending losses

30. Fiber-Optic Cable (Connectors)

31. Advantage of optical fiber
communication
1) The life of fiber is longer than copper wire
2) Handling and installation costs of optical fiber is
very nominal
3) It is unaffected with electromagnetic interference
4) Attenuation in optical fiber is lower than coaxial
cable or twisted pair.
5) There is no necessity of additional equipment for
protecting against grounding and voltage
problems.
6) As it does not radiates energy any antenna or
detector cannot detects it hence provides signal
security