Abstract

A heterodyne optical receiver configuration employing incoherent demodulation consists of a bandpass intermediate frequency (IF) filter and an envelope detector followed by an integrator and data discriminator. A direct detection system employing a filtered optical preamplifier also employs these elements. It has been shown both theoretically and experimentally that such systems require careful optimization of both the IF filter bandwidth and the decision threshold to achieve optimum performance. While the theoretical treatments to date have been insightful, they have not allowed straightforward analytic treatments or simple computations of the output probability distributions. In this paper we apply the method of characteristic functions to a solution of the problem of phase noise in an incoherent linear envelope detection system. This approach was first used many years ago and has been described in well-known textbooks but has never, to our knowledge, been applied to the problem of phase noise. The method has the advantage over other approaches of analytically providing the eigenvalue equations for the poles of the characteristic function of the output probability distributions, allowing accurate system analysis without the necessity of long computation time.

© 1989 Optical Society of America