3. What is Optical Fiber ?
⚫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 distance.
5. Main parts:
⚫Core- central tube of very thin size made up of
optically transparentdielectric mediumand carries
the light form transmitter to receiver. The core
diametercan vary from about 5um-100 um.
⚫Cladding- outeroptical material surrounding thecore
having ref lecting index lowerthan core. It helps to
keep the light within the core throughout the
phenomenaof total internal reflection.
⚫Buffer Coating- plasticcoating thatprotects the fiber
made of silicon rubber. The typical diameter of fiber
aftercoating is 250-300um.
6. Working principle
⚫ Total Internal Reflection:
⚫ 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
fiber is bend.
8. Classification of optical fiber
⚫Optical fiber is classified into twocategories based
on:-
The numberof modes-
Single mode fiber(SMF)
Multi-mode fiber(MMF)
9. On basis of number of modes:-
Single mode fiber-
In single mode fiberonlyone modecan propagate through the
fiber.
It has small corediameter (5um) and high cladding diameter
(70um).
Difference between the refractive index of coreand cladding is
very small.
There is neitherdispersion nordegradation therefore it is suitable
for long distancecommunication.
The light is passed through the single mode fiber through laser
diode.
10. Multi- mode fiber
Itallows a large numberof modes for
lightray travelling through it.
Thecorediameter is 40um and that
of cladding is 70um.
The relative refractive index
difference isalso large than single
mode fiber.
There is signal degradationdue to
multimodedispersion.
It is not suitable for long distance
communication due to large
dispersion and attenuation of signal.
11. Optical Fiber Communication
System
⚫Information source- it providean electrical signal toa
transmittercomprising an electrical stage.
⚫Electrical transmitter- It drives an optical source to givean
modulation of the lightwave carrier.
⚫Optical source- It provides the electrical-optical
conversion. It may bea semiconductor laseroran LED.
12. Continue..
Optical cable- It serveas transmission medium.
Optical detector- It is responsible foroptical toelectrical
conversion of data. It may bea photodiodes, phototransistors or
photoconductors.
Electrical receiver: It is used forelectrical interfacing at the
receiver end of the optical link and to perform the signal
processing electrically.
Destination: It is the final pointatwhich we receive the
information in the formof electrical signal.
13. Advantage of Optical Fiber
Immense bandwidth toutilize
Total electrical isolation in the transmission medium
Very low transmission loss
Small size and lightweight
High signal security
Very low powerconsumptionand wide scopeof
systemexpansion etc.
14. Disadvantage
1) System installation isverycostly.
2) Onlypoint-to-pointcommunication is possible.
3) Preciseand costly instrumentswould be required.
4) Splicing is timeconsuming.
5) Itacceptonly unipolarcodes.
15. References:
J. Gower, optical communication systems, 2nd ed,
prentice hall, London
principles of communication systems: herbt taub and
Donald L.schilling
telecommunications engineers reference book:
fradian mazda
16. Team work
• 1. Abdelhadi wael Abdelhadi
2.ziad ahmed Abdelaziz
3.Abdelrahman Mohamed abo draz
4.ziad ahmed mohamed
