Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 4

An engineer has the following components available:
( a ) GaAlAs laser diode operating at 850 nm and capable of coupling 1 mW (0 dBm) into a fiber.
( b ) Ten sections of cable each of which is 500 m long, has a 4-dB/km attenuation, and has connectors on both ends.
( c ) Connector loss of 2 dB/connector.
(d) A pin photodiode receiver.
( e ) An avalanche photodiode receiver.
Using these components, the engineer wishes to construct a 5-km link operating at 20 Mb/s. If the sensitivities of the pin and APD receivers are -45 and -56 dBm, respectively, which receiver should be used if a 6-dB system operating margin is required