Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 9

Consider an avalanche photodiode receiver that has the following parameters: dark current I D = 1 nA, leakage current I L = 1 nA, quantum efficiency = 0.85, gain M = 100, excess noise factor F = M 1/2 , load resistor R L = 10 4 , and bandwidth B e = 10 kHz. Suppose a sinusoidally varying 850-nm signal having a modulation index m = 0.85 falls on the photodiode, which is at room temperature ( T = 300 K). To compare the contributions from the various noise terms to the signal-to-noise ratio for this particular set of parameters, plot the following terms in decibels [i.e., 10 log( S / N )] as a function of the average received optical power P 0. Let P₀range from -70 to 0 dBm; that is, from 0.1 nW to 1.0 mW:
( a )
( b )
( c )
( d )
What happens to these curves if either the load resistor, the gain, the dark current, or the bandwidth is changed