Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 05

Years: MAY 2016

1. Intramodal dispersion:

Pulse broadening within a single mode is called as intramodal dispersion or chromatic dispersion. The two main causes of intramodal dispersion are as follows:

a. Material dispersion:

• It is the pulse spreading due to the dispersive properties of material.

• It arises from variation of refractive index of the core material as a function of wavelength.

b. Waveguide dispersion:

• It occurs because a single mode fiber confines only about 80% of the optical power to the core.

• Dispersion thus arises since the 20% light propagating in the cladding travels faster than light confined to the core.

1. Intermodal dispersion:

• Dispersion caused by multipath propagation of light energy is referred to as intermodal dispersion.

• In digital transmission, we use light pulse to transmit bit 1 and no pulse for bit 0.

• When the light pulse enters fiber it is breakdown into small pulses carried by individual modes.

• At the output individual pulses are recombined and since they are overlapped receiver sees a long pulse causing pulse broadening.