Receiver Design for Optical PPM Systems

An optimum receiver structure for optical PPM systemics is considered and from this a simple sub-optimum receiver is proposed which offers significant SNR improvement relative to existing design approaches and yet requires few circuit changes. Receivers incorporating either p-i-n or avalanche photodiodes and FET or BJT preamplifiers are analyzed. The optimization technique relies on matching the frequency response of the receiver to that of the incident optical pulse and setting the avalanche gain and threshold detector at optimum levels. For a FET preamplifier the SNR improvement is 10.8 dB with a p-i-n photodiode and 4.7 dB with an avalanche photodiode. For a BJT preamplifier the SNR improvement is 3.1 dB and 2.3 dB with the p-i-n and avalanche diodes, respectively.