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Iqbal Ahmed Assistant Professor Dept. of Computer Sci. & Engg. University of Chittagong

Optical Fibres

Strength Member

Sheath 1 Aluminum Tape Sheath 3

Sheath 2 Steal Wire Reinforcement

Introduction  Optical Fiber It is a glass filament or wire which carries light.  It is a cylindrical waveguide that operate at optical frequency.  It confines electromagnetic energy in the form of light. 

● COMMUNICATION  It may be broadly defined as the transfer of information from one point to another.


Light is the form of electromagnetic Wave just as waves, but with high frequency and shorter

wavelength. Spectrum



100 KHZ to1 THZ

3KM to 300 µm

Infra Red light Optical Communication

1 THZ to 100 THZ 176 THz to 375 THZ

300 to 3 µm 1.7 to 0.8 µm

1550 nm Window 1310 nm Window 850 nm Window Visible Light

193.5 THz 230 THz 353 THz 428 to 750 THZ

1.550 µm 1.310 µm 0.85 µm 0.7 TO 0.4 µm

UV,X & γ rays

750 to 10 7 THZ

0.4 to 3x10 - 6 µm

Radio waves

Optical Fibre Communication 1.7 µm


Short wave






3000 km

30 km



~0.7 µm

~0.4 µm

Gamma Rays




Far infrared




1010 1012 1014


300 m


3 cm

30 nm

f = 1/T

Cosmic rays



Standard Long wave


0.8 µm

0.3 mm

3 µm

λ = c/f

1018 0.3 nm

1020 1022

Frequency (Hz)

3 pm 0.3 pm

c = 3x10 m/s 8


HISTORY  Hollow Logs, Drum (different sizes), Wind

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Instruments (pipes), Smoke Signals, Signal fires and Signaling lamps. The first optical fiber exhibited very high attenuation i.e. 1000 dB/Km. While coaxial cable losses were 5-10 dB/Km. Fiber losses were reduced to below 5 dB/Km. Development of fiber waveguides with optical frequencies at small wavelengths requires the development of all optical components. Laser Life at the start was 1000 Hrs & now is 100 years. At present two optical windows are in operation i.e. 1310 nm ,1550nm.

Advantages of Optical Fiber  Enormous potential bandwidth

The maximum capacity of single mode step index fiber is 1.6 Tb/Sec w.r.t coaxial cable bandwidth of 500 MHZ.  Small size and weight Optical fibers have very small diameter i.e. 125um which is just like a human hair while the dia of one copper is 0.8mm.The ratio of weight as compared to other cables is 25:1.  Electrical isolation Optical fibers are fabricated from glass which are electrical insulated hence they don't exhibit interference problem.

Advantages of Optical Fiber  Immunity to Interference & Cross talk

The material of optical fiber is dielectric/glass hence there is no possibility of cross talk or leakage.  Signal Security The light from optical fibers doesn't radiate significantly and therefore they provide a high degree of signal security.  Low transmission loss Laser light travels with high speed on pure transparent glass. This development of optical fiber over the last twenty years has resulted in the production of O/F cables with very low attenuation i.e. 0.2 dB/Km.

Advantages of Optical Fiber ď‚— Ruggedness & Flexibility

Cable structures have been developed which have proved flexible, compact & extremely high. ď‚— System Reliability & Ease of Mtce Due to low transmission loss, intermediate repeaters & line amplifiers are reduced. Hence with few repeaters system reliability is generally enhanced. The optical component life time is 20 to 30 years. ď‚— Potential Low Cost The glass which generally provides the optical fiber transmission medium is made from sand which is available in abundance.

Disadvantages of Optical Fiber  Very small hole on the surface of fiber may weakens the     

tensile strength. A small bend on optical fiber causes radiation loss. Alignment problem, connectors & core misalignment. The cost of fusion splicing is high. The fault localization is some what difficult. Clean environment is required during splicing. A small dust particle can create high attenuation.

Books Refernce: 1. Optical Fiber Communications: Priniciples and

Practice John M Senior 2. Optical Fiber Communications: Gerd Keiser

Optical Fiber Slide 01