A multimode step index fiber has source of RMS spectral width of 60nm and dispersion parameter for fiber is 150psnm -1 km -1 . Estimate rms pulse broadening due to material dispersion.

Optoelectronics and Optical Communication 

A multimode step index fiber has source of RMS spectral width of 60nm and dispersion parameter for fiber is 150psnm -1 km -1 . Estimate rms pulse broadening due to material dispersion.

a) 12.5ns km -1 
b) 9.6ns km -1 
c) 9.0ns km -1 
d) 10.2ns km -1

Answer : - 9.0ns km -1

The RMS pulse broadening per km due to material dispersion is given by 
σ m (1 km) = σ λ LM 
= 60*1* 150pskm -1 
= 9.0nskm -1 
Where σ λ = rms spectral width 
L = length of fiber 
M = dispersion parameter.