Electronic Dispersion Compensation And Carrier Phase Estimation In High Speed Coherent Optical Transmission System

Coherent detection employing multilevel modulation format has become one of the most promising technologies for next generation high speed transmission system due to the high power and spectral efficiencies. With the powerful digital signal processing (DSP), coherent optical receivers allow the significant equalization of chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise (PN) and nonlinear effects in the electrical domain. Recently, the realizations of these DSP algorithms for mitigating the channel distortions in the transmission system are the most attractive investigations in optical communication techniques.In this dissertation, we present a comparative analysis of three digital filters for chromatic dispersion compensation, an analytical evaluation of carrier phase estimation with digital equalization enhanced phase noise (EEPN) and a brief discussion for PMD adaptive equalization. To implement these investigations, a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system is realized in the VPI simulation platform. Based on this coherent communication system, we have completed the following work:From the aspect of chromatic dispersion compensation, several popular CD equalizers have been compared in the coherent transmission system by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations and their computational complexity. The upper and the lower bounds of the required tap number in the time-domain CD equalization, the minimum overlap and the optimum fast Fourier transform (FFT) length in the frequency-domain CD equalization are determined in both theoretical calculation and numerical simulations.We present an analysis of carrier phase estimation with digital equalization enhanced phase noise (EEPN) in the high speed coherent transmission system. Meanwhile, we investigate the enhancement of laser phase noise due to different digital dispersion compensation methods. For the first time to our knowledge, we find that both the transmitter and the local oscillator phase fluctuations can be equally enhanced by the least mean square (LMS) dispersion equalization. The bit-error-rate (BER) floor in carrier phase estimation using the one-tap normalized LMS filter, the differential phase detection, the block average method and the Viterbi-Viterbi method are evaluated analytically. The theoretical predictions make a good agreement with the numerical simulations.