Optical Fiber communication

1. By:
Amjad Hassan Khan MK
Lecturer in Electronics
Kristu Jayanti College, Bengaluru

3. Greater information capacity
Immense bandwidth to utilize
Total electrical isolation in the transmission medium
Immunity to interference and crosstalk
High signal security
Very low power consumption and wide scope of
system expansion etc.
Very low transmission loss
Small size and light weight
Longer Distance

4. Fragility
Physical Strength of cable is less
Difficult to Install
Attenuation & Dispersion
Specialized tools, equipment and trained people is
required
Interfacing cost is high
Medical
Defense/Government
Data Storage
Telecommunications
Networking
Industrial/Commercial
Broadcast/CATV

5.  A fiber Optic Communication System uses light wave technology to
transmit the data over a fiber by changing electronic signals into
light.
 An optical fiber is essentially a waveguide for light. It consists of a
core and cladding that surrounds the core.
 The index of refraction of the cladding is less than that of the core,
causing rays of light leaving the core to be refracted back into the
core
 When a ray of light travels from a denser to a rarer medium such that
the angle of incidence is greater than the critical angle, the ray
reflects back into the same medium this phenomena is called total
internal reflection.
 In the optical fiber the rays undergo repeated total number of
reflections until it emerges out of the other end of the fiber, even if
the fiber is bent.
 A light-emitting diode (LED) or laser diode (LD) can be used for the
source

7. Conditions for TIR
• η1 > η2
• ϕi > ϕc

8. Maximum Acceptance Angle (θ0max):
Numerical Aperture (NA):

10. • An optical fiber is a hair thin cylindrical fiber of glass or any
transparent dielectric medium.
• The fiber which are used for optical communication are wave guides
made of transparent dielectrics.
• Its function is to guide visible and infrared light over long distances.

11. There are two types of optical fiber:-
Step-index optical fiber
Graded-index optical fiber
Classifications:
• Core – central tube of very thin size made up
of optically transparent dielectric medium and
carries the light form transmitter to receiver. The
core diameter can vary from about 5um to 100um
• Cladding – outer optical material surrounding the
core having reflecting index lower than core.
It helps to keep the light within the core throughout the
phenomena of total internal reflection.
• Buffer Coating – plastic coating that protects the fiber made of
silicon rubber. The typical diameter of fiber after coating is 250-
300 um.

14. The light produced by them should be monochromatic
The light source should have high-output intensity
The devices should be small and easily coupled
They must be relatively inexpensive to manufacture.
Typical light sources include:
 Light-Emitting Diodes
 Laser Diodes
Light-Emitting Diodes:
• An LED is form of junction diode
that is operated with forward bias
• Instead of generating heat at the
PN junction, light is generated
and passes through an opening or lens
• LEDs can be visible spectrum or infrared

15. LASER Diodes:
• Light Amplification by Stimulated Emission of Radiation
• made from Aluminum Gallium Arsenide (AlGaAs) and Gallium
Arsenide (GaAs)

16. • The basic optical receiver converts the modulated light coming
from the optical fiber back into a replica of the original signal
applied to the transmitter.
• The most common optical detector used with fiber-optic systems
is the PIN diode
PIN diode:-

17. Avalanche Photo Diode :(APD)
An avalanche photo diode (APD) is a PiPN device as shown in fig

18.  RAYLEIGH SCATTERING LOSSES
 ABSORPTION LOSSES
1. Ultraviolet absorption
2. Infrared absorption
3. Ion resonance absorption
 ION RESONANCE ABSORPTION
 BENDING LOSSES
1. Micro bending
2. Macro bending