Researches On DQPSK Modulation And PMD Compensation In Optical Fiber Communication Systems

With the growth of traffic in data and video transmission, the transmission rate of each channel and the number of wavelength division multiplexing (WDM) channels of optical backbone network are improving gradually. The research on 40Gb/s or 100Gb/s transmission technology in a single-channel has been a hot spot. For high-speed optical transmission system, CD, PMD, nonlinear effects and ASE are considered to be the main obstacles which limit the transmission capacity. It has been more and more urgent to compensate the signal impairments producing by CD, PMD in high-speed optical transmission system.For the signal impairments in high-speed optical communication system, there are two kinds of solutions:1. Using a novel modulation format to resist the signal impairments;2. Design an electrical equalizer or optical compensator to weaken or eliminate the signal impairments;Based on the proposed solutions, the research works and innovations in the dissertation are summarized as follows:1. The modulation and demodulation of differential quadrature phase shift keying (DQPSK) are analyzed in detail. And the formula of the differential precoder is deduced. At last, the performance of the DQPSK transmission system is studied, of which the PMD tolerance is 17ps;2. One kind of parallel DQPSK differential precoding algorithm based on the parallel prefix network (PPN) structure is proposed, and this novel algorithm is verified using 2Mb/s data stream. The parallel DQPSK differential precoding of 20Gb/s data based on the platform of Xilinx Virtex5 FX100T FPGA has been completed;3. The basic concepts and measurement methods of PMD are reviewed and summarized. The PMD compensation technologies are discussed in detail. The principle and advantages of optical PMD compensation which using DOP as the feedback signal and PSO as the feedback algorithm is studied;4. The hardware system of PMD compensation unit and PMD monitoring unit are implemented. An adaptive PMD compensator is implemented. It can be used in a single-channel,40Gb/s DWDM system;5. Involved in setting up a 20Gb/s NRZ-DQPSK modulation system, 1st-order PMD compensation is demonstrated experimentally. Experimental results show that the PMD compensator can track the average polarization state variation at 65rad/s without any lost of the optimum tracking, and the compensator can increase the maximal tolerable PMD value by 26ps from 17ps to 43ps in 1dB OSNR conditions. The adaptive PMD compensator's response time is less than 1ms, and the average compensation time is less than 8ms.