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.

We consider the design and implementation of a lownoise feedback receive amplifier for use in optical communication systems. The feedback amplifier configuration is advantageous in that it offers a wide bandwidth with good signal to noise ratio.

A Percival coil connected between the photodetector and amplifier in the receiver of a digital optical communication system offers the possibility of a reduced signal power requirement for a given bit error rate. When the photodetector is an avalanche diode, the modified receiver requires a lower value of avalanche gain for optimum performance.

We consider the design of a receiver for a digital optical fiber system operating with multilevel pulse amplitude modulation. This form of modulation provides for high bit rates on digital systems employing large diameter optical fibers and LED sources. The receiver configuration analysis is one with a p-i-n avalanche photodetector and a FET preamplifier. The analysis is complicated by the fact that the signal levels and threshold boundries have to be nonuniformly spaced to cope with signal dependent shot noise introduced by the photodiode detector. An algorithm for level placement is reported. Performance figures for typical systems, with optical pulse shape which are either Gaussian or exponential, are calculated.