A discrete time simulation is used to evaluate the effects of restricted bandwidth on an optical DPSK system [Fig. 1(a)]. This is done by studying how the SNR penalty changes as a function of baseband (transmitter and receiver) and IF bandwidths. A lower bound for the signal power is obtained as the square of the minimum signal level at the optimum sampling time. The optimum sampling is found by maximizing the signal power. For the noise power, only the shot-noise contribution is considered, modeled as a zero mean Gaussian process with a flat frequency spectrum, filtered by the IF filter and the post DPSK demodulator filter.
© 1988 Optical Society of AmericaPDF Article