On the Accuracy of the Gaussian Approximation for Performance Estimation in Optical DPSK Systems with In-Band Crosstalk

The Gaussian approximation is known to be quite accurate for estimating the system performance of an optically pre-amplified on-off keying (OOK) system in the presence of multiple in-band interferers. This paper assesses if similar accuracy can be also achieved in an optically pre-amplified differential phase-shift keying (DPSK) system. The probability density function of the decision variable at the receiver is computed as a function of the number of interferers, and it is observed that this variable statistic is clearly non-Gaussian even for a large number of interferers. It is also shown that, for a 1 dB power penalty and a 16 interferer scenario, the Gaussian approximation over-estimates the real value of the total crosstalk level by as much as 3.7 dB for DPSK signals, while for OOK signals this gap shrinks by approximately 2 dB.