Receiver Design for Multilevel Digital Optical Fiber Systems

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.