Mititgation of Transmission Impairments for Phase-encoded Optical Communcation Systems by Optimized Digital Backward Propagatioin

In this section, the simulation analysis for RZ-DQPSK single-channel phase-encoded transmission systems with DBP compensators on the receiver side for different launch powers with increasing numbers of calculation steps per fiber span has been presented. A computationally simpler algorhithm for solving the NLSE based on a modified split-step Fourier method was used.

As result, the improvement in the quality of the transmitted signals for various launch powers can be achieved by using DBP compensators with an increasing number of calculation steps per fiber span. The linear an nonlinear effects can be compensated very effectively with the DBP algorithm for different launch powers, where dispersion, the non-linear coefficient parameter (NL) and the non-linear operator calculation point (NLpt) are optimized.

The fact, that increase the number of steps per span using DPB leaeds to improvement in the quality of transmitted signal varying degrees, it is the thresholds of different launch powers illustrates. The different thresholds at 5, 12 and 20 calculation steps per fiber span show that the signal distrotion cannot be compensated entirely with greather launch powers, because the stronger Kerr effect of nonlinearity makes it impossible, as nonlinear distortion increases very quickly at higher launch powers. For lower powers, i.e. of 9 dBM, the EO improvements are very effectivly, meaning that the linear and Kerr nonlinearity effects are almost compensated for in the DBP algorithm. For higher launch powers, i.e. 12 dBm, the EO-improvement can be achieved only by three-quarters. Higher launch powers will lead to the recovery of transmitted signals being destroyed because the information capacity whithin the fiber is limited by stronger Kerr nonlinearities.