Consider an optical communication system operating at λ=800nm. Suppose only 1 % of optical frequency is available for channel bandwidth for optical communication. If number of channels can be accommodated for transmitting audio signals required a bandwidth of 5 kHz is y×107,  then y is

Bandwidth of channel  = 5 kHz = 5000 HZ  Optical wave length  = λ=800nm =8×10−7m  Optical frequency  =n=Cλ = 3×1088×10−7=0.375×1015 Hz  1 % of frequency is available, so  n = 1 % of  0.375×1015                                                                  = =375×1010 Hz    No of channels   =Total bandwidthBandwidth per channel  =375×10105000=75×107