Mitigating fiber nonlinearity in multidimensional modulation-based optical communication systems by phase-conjugated twin waves technique

Abstract

Next-generation optical networks must be flexible and efficiently utilize the available spectrum to enhance spectral efficiency and network capacity. Future optical transmission should adapt its bit rate and reach according to network demands by employing multidimensional modulation formats while maintaining low costs and complexity for practical implementation. In this paper, we utilize a phase-conjugated twin waves (PCTWs) technique to eliminate nonlinear phase noise (NLPN) in optical transmission systems that employ multidimensional modulation formats. Four-dimensional (4D) modulation formats, namely, Ball, Cluster, polarization-switched (PS)-quadrature phase shift keying (QPSK), and 32 set partitioning (32SP)-16 quadrature amplitude modulation (16QAM), are employed to modulate signals transmitted over long-haul fiber links. In the proposed system, the twin signals are spatially propagated over two similar optical links at a rate symbol rate of 20 Gsymbol/s. At the receiver, the PCTWs are recovered and then coherently combined for mitigating the effects of NLPN and improving a signal-to-noise ratio (SNR). The results indicate that the PCTWs technique enhances system performance for all four 4D modulation formats. Specifically, the achievable reaches is extended by 55 % for PS-QPSK, 48 % for 32SP-16QAM, 18 % for Custer, and 27 % for 8-Ball at a bit error rate (BER) of 10⁻³. Notably, the PCTWs technique considerably enhances the performance of PS-QPSK system, while the lowest improving is observed with the Cluster communication format when using the PCTWs technique.