Applicability of Gaussian Noise Approximation for Optically   Pre-Amplified DPSK Receivers with Balanced Detection
  This letter presents a comparison of exact probability density function with the Gaussian noise approximation in optically pre-amplified DPSK receivers with optical Mach-Zehnder interferometer demodulation (MZI) and balanced detection, including the impact of phase noise. It is found that the Gaussian noise approximation significantly over-estimates ASE-ASE beat noise in DPSK receivers with balanced detection particularly when phase noise is negligible, compared to IM/DD receivers, ASE- amplified spontaneous emission. However, the Gaussian noise approximation is still applicable for DPSK receivers with balanced detection and the measured 3-dB advantage is predicted by the Gaussian noise distribution. 
Xiupu Zhang, Zhenqian Qu, Guodong Zhang, Guangxue Yang