Abstract

A comprehensive theoretical analysis of noise statistics in optically pre-amplified DPSK receivers with optical Mach-Zehnder interferometer demodulation is presented for the first time. For such a receiver, there are three dominant noise sources which degrade the performance of DPSK systems: signal-ASE beat noise, ASE-ASE beat noise, and nonlinear phase noise. The first two noise sources are added to the signal, and thus they can be referred to as linearly additive noise. The detailed derivations of the exact noise statistics considering both the linearly additive noise and nonlinear phase noise are given in this thesis. Due to simplicity, the Gaussian approximation has been widely used in the case of optical systems with intensity modulation and direct detection (IM/DD). Therefore, the Gaussian approximation of noise statistics is also given and compared with the exact noise statistics in DPSK receivers. Numerical calculations show that the exact noise statistics are quite different from the Gaussian approximation, particularly for DPSK receivers with balanced detection. The numerical results of probability density functions and bit error rate with the exact noise statistics are in good agreement with the published experimental results. A comparative study of noise statistics in both DPSK and IM/DD receivers is also given.