Long-haul 112 Gbit/s coherent polarization multiplexing QPSK transmission experiment on G.652 fiber with the improved DSP unit

An improved DSP unit with a joint timing recovery and equalization scheme is proposed to remove the adverse interaction of timing recovery and adaptive equalization. The joint scheme consists of two novel algorithms we proposed. One is the all-digital timing recovery loop which is not sensitive to the nonideal characteristics of the analog device. The other is BER aided CMA (BA-CMA) which can solve the problem of ill-convergence of the polarization component. The simulating result shows that the joint scheme is more effective than the independent scheme. A long-haul 112 Gbit/s coherent PM-QPSK transmission experiment on G.652 SSMF employing the improved DSP unit is reported. The experimental results illuminate that the DSP unit we employed is effective. The results of the experiment showed that the method of CD compensation at optical domain was contrasted with the method at electrical domain, electrical equalization was illuminated a better method. In addition, the results also illuminate that RZ system can mitigate nonlinearity better than NRZ system, and DQPSK format has worse BER performance than QPSK format.