Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 12

A 90-Mb/s NRZ data transmission system that sends two DS3 (45-Mb/s) channels uses a GaAlAs laser diode that has a 1-nm spectral width. The rise time of the laser transmitter output is 2 ns. The transmission distance is 7 km over a graded-index fiber that has an 800-MHz km bandwidth-distance product.
( a ) If the receiver bandwidth is 90 MHz and the mode-mixing factor q = 0.7, what is the system rise time Does this rise time meet the NRZ data requirement of being less than 70 percent of a pulse width
( b ) What is the system rise time if there is no mode mixing in the 7-km link; that is, q = 1.0