Nonbinary LDPC-Coded Mode-Multiplexed Coherent Optical OFDM 1.28-Tbit/s 16-QAM Signal Transmission Over 2000 km of Few-Mode Fibers With Mode-Dependent Loss

We demonstrate the possibility of nonbinary LDPC-coded mode-multiplexed coherent optical OFDM 1.28-Tbit/s 16-QAM signal transmission over 2000 km of few-mode fiber (FMF) with mode-dependent loss (MDL) by using an advanced mode-coupling compensation scheme. The performance of proposed coded-modulation scheme is evaluated for different number of spatial modes. The simulation results indicate that the MDL is the predominant effect in the long-haul optical transmission based on FMFs. Different pilot-aided OFDM based compensation methods are studied, and it has been found that minimum mean-square estimation with linear interpolation method is the most robust against mode coupling and MDL. We also show that the nonbinary LDPC-coded modulation provides about 1 dB improvement over binary LDPC-coded modulation (16 QAM OFDM and MDL of 25 dB). Finally, we study the degradation of increasing the number of modes and investigate the proposed scheme for different MDL values in both fourand eight-mode fibers.