Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 9

For a bit error rate of 10 -9 assume that the combined spectral width of the signal carrier wave and the local oscillator should be 1 percent of the transmitted bit rate.
( a ) What spectral width is needed at 1310 nm for a 100-Mb/s data rate
( b ) What is the maximum allowed spectral width at 2.5 Gb/s