Compensation Of Dispersion And Nonlinearity In High-speed Fiber Communication Systems

Fiber group-velocity dispersion (GVD), fiber nonlinearity and their interaction become the essential limiting factors of fiber communication systems with the increasing of bit rate and transmission distance. This dissertation undertakes a detailed study of GVD and fiber nonlinearity compensation schemes in 10 Gb/s and 40 Gb/s long-haul fiber transmission using direct detection or coherent detection. The study is carried out through theoretical analysis, numerical simulation and experimental demonstration. The main points are as follows:1. A new method to improve dispersion tolerance by imposing phase pre-modulation on non-return-to-zero (NRZ) format is put forward in this dissertation. 40 Gb/s simulation and 10 Gb/s experiment are performed using tunable clock or data-related signal as the phase pre-modulating signal. The eye opening and receiver sensitivity are improved and the dispersion tolerance is doubled when the phase pre-modulation is imposed on NRZ signals. This scheme relaxes the requirement of optical signal-to-noise ratio and dispersion management. It also benefits the NRZ system upgrade because the phase pre-modulation is easy to be employed and adjusted at the transmitter.2. A means using coherent optical time-domain sampling (COTDS) for parallel electronic dispersion compensation (EDC) is firstly presented in digital signal processing (DSP)-based high-speed optical coherent detection. The rigid requirement for high-speed analog-to-digital converters (ADCs) and DSP units is relaxed by using COTDS combined with parallel signal processing. Parallel EDC using 10 Gsample/s ADCs instead of 20 Gsample/s ADCs is experimentally demonstrated for 10 Gb/s DPSK signal. It provides an effective solution for EDC in high-speed optical coherent detection.3. A new scheme is proposed using terminal dispersion compensation instead of inline dispersion compensation scheme in 40 Gb/s transmission over standard single-mode fiber (SSMF). Simulation and experiment of 40 Gb/s signals in long-haul transmission demonstrate the terminal dispersion compensation scheme is more resistant to fiber nonlinearities. The Q value of the terminal compensation scheme is around 2 dB higher than that of the inline compensation scheme in nonlinear region after 1,500 km transmission. It provides a new avenue to design 40 Gb/s fiber transmission links with simplicity, flexibility and potential low cost.4. The algorithm of carrier phase estimation in differential coding/coherent detection systems is modified to improve the resistance to intrachannel fiber nonlinearities. Simulation results of 20 Gb/s DQPSK transmission show that coherent detection is less resistant to intrachannel nonlinearities than differential detection. The reason is the nonlinear phase-shift correlation between adjacent symbols helps differential detection partially cancel the nonlinear phase noise while does not benefit coherent detection. With the modified algorithm of carrier phase estimation, coherent detection has similar performance to differential detection in nonlinear region while keeps the advantage in linear region. Therefore, the performance of coherent detection over the whole power range is improved.