Calculation of Bit Error Ratio for Optically Pre-Amplified DPSK   Receivers Using Optical Mach-Zehnder Interferometer Demodulation and Balanced   Detection
  This paper presents an analysis of how to calculate bit error ratio (BER) with physical explanation for optically pre-amplified DPSK receivers using optical Mach-Zehnder interferometer (MZI) demodulation and balanced detection. It is shown that BER calculation method for this kind of receivers is different from the conventional calculation method used widely for IM/DD receivers. An analytical relationship in receiver sensitivity between DPSK receivers using MZI demodulation with balanced detection and IM/DD receivers (or DPSK receivers using MZI demodulation and single-port detection) is given based on the Gaussian noise approximation. Our calculation method correctly predicts the 3-dB improvement of receiver sensitivity by using balanced detection over single-port detection or IM/DD receivers. Furthermore, quantum-limited DPSK receivers with MZI demodulation are also analyzed. 
Xiupu Zhang, Zhenqian Qu, and Lei Wang