Optical Fiber Communications 4th Edition by Gerd Keiser

Exercise 6

Consider a 32-channel FDM system with a 4.4-percent modulation index per channel. Let RIN = -135 dB/Hz, and assume the pin photodiode receiver has a responsivity of 0.6 A/W, B e = 5 GHz, I D = 10 nA, R eq = 50 W, and F t = 3 dB.
( a ) Find the carrier-to-noise ratio for this link if the received optical power is -10 dBm.
( b ) Find the carrier-to-noise ratio if the modulation index is increased to 7 percent per channel and the received optical power is decreased to -13 dBm.