Research On Signal Distortion Compensation Method For Digital Coherent Optical Receivers

With the development of mobile Internet, high-definition vedio and big data services, the demand for data transmission bandwidth and rate increases greatly, This promotes the development of the optical fiber communication systems toward the direction of ultra-high-speed, ultra-large-capacity, and dynamically re-configurability. Coherent optical communication technology has the merits such as compatibility with different advanced modulation formats, high spectral efficiency, high sensitivity and high wavelength selectivity. Moreover, coherent detection technology can recovery the amplitude, phase and polarization of optical carrier, in combination with DSP technology, the various distortions from fiber channel and optical transmitter/receiver module can be compensated effectively. Thus coherent optical communication technology has been considered as one of the key technologies for the next generation optical network.In this thesis, a set of methods are proposed for various kinds of signal distortions compensation for digital coherent receiver. Simulation platforms of the coherent optical communication and digital signal processing unit is set up based on VPI TransmissionMaker 9.1 and Matlab to test the effectiveness of the algorithms. First, the optical signal distortions compensation technologies based on digital coherent receiver are reviewed. Next, the impact of nonlinear effect, chromatic dispersion in optical fibers and laser phase noise are studied based on the theoretical model of these devices. Then, a method for carrier phase recovery based on Viterbi-Viterbi algorithm is studied. By using auto correlation zero forcing and constellation noise cloud circularity optimization algorithms to realize the adaptive optimization of average window length is realized, improving the tracking speed and compensation precision of phase noise. After that, by taking full advantage of the amplitude, phase and spectrum information of pilot tone, a method for joint adaptive compensation of multiple distortions, including CD, LFO, LPN and XPM is proposed. Finally, the method for intra-channel nonlinear distortions(SPM) compensation based on phase-conjugated pilot tones is investigated. It can effectively enhance the optimum launch power and reduce the loss of spectrum efficiency from the insertion of pilot tone.