Receiver Designs for Fiber Optic Communications Optimization in Terms of Excess Noise Factors That Depend on Avalanche Gains

The optimizations of signal-to-noise ratios (SNR's) and pulse error rates in fiber optic receivers are investigated in terms of an avalanche photo diode (APD) model in which excess noise factors depend on the avalanche gains. The optimization of SNR results in an analytical solution for the optimum avalanche gain. A numerical example compares the result with those of conventional SNR optimization where excess noise factors do not depend on avalanche gains. Improvements of around 2 dB in the accuracy of the optimum SNR's are expected. It is shown that the optimization of pulse error rates for digital transmissions can not be attained analytically. This problem is solved by the use of approximate representations of excess noise factors. Two approximate representations are illustrated that provide very simple and accurate analytical solutions. Numerical examples demonstrate the efficacy of these approximate solutions.