Signal-to-noise ratio for lightwave systems using avalanche photodiodes

An expression for the signal-to-noise ratio (SNR) at the output of an avalanche photodiode (APD) receiver is derived that includes the effects of photoinjected carriers, dark-generated carriers, and the receiver circuitry. It is found that the dark current alters both the magnitude of the SNR and the value of the mean multiplication where the SNR achieves its maximum value. The formula differs from the expression that is conventionally used (S.M. Sze, 1981) in that it makes use of different excess noise factors for photo-generated and dark-generated carriers.<
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