Expressions are obtained for the probability of error of a binary intensity-modulated direct-detection optical communication system consisting of an ideal photodetector followed by a nonideal photoelectron counter, in this case anRClow-pass filter. Calculation of probability of error requires the determination of the output statistics of the nonideal counter. Numerical techniques are used to evaluate the expression for probability of error and optimum thresholds as a function of signal level. The optimum filter bandwidth required to simulate an ideal counter is also evaluated numerically. Results indicate that, for the particular case considered, the nonideal receiver requires an additional 1 dB of signal power to achieve performance equivalent to the ideal receiver.

Digital baseband and digital subcarrier noncoherent optical communication systems are considered in this paper. Expressions are developed for the bit error probability of optical subcarrier systems which use a nonliner polarization modulator and either a one-detector or a two-detector receiver, The expressions are evaluated numerically, and the results are used to compare the one- and two-detector subcarrier systems with the corresponding one- and two-detector baseband systems for a fLxed bit error probability.