Dependence of optical receiver sensitivity, in a 147.75 Mb/s heterodyne DPSK system, as a function of optical and electrical parameter variations.

Measurements of the changes in receiver sensitivity caused by a) the effect of band-pass and low pass filtering, b) the dependence on integer and non-integer values of the intermediate frequency to bit rate ratio, c) the influence of local oscillator power and d) the impact of deviation from ideal pi phase-shift modulation are described. The results were taken with external cavity lasers for which the laser phase noise was negligible.