An 8-dimensional Modulation Format for Mitigating the NPSE in the Polarization Multiplexing Coherent System

For the wavelength division multiplexing coherent optical communication system, we use an 8-dimensional modulation coding method to reduce the inter-channel nonlinear interference. The 8-dimensional modulation format enables the degree of polarization of the 8-dimensional symbol composed of four 2-dimensional symbols of adjacent time slots equal to 0, thereby effectively suppressing the nonlinear polarization scattering effect (NPSE) caused by the inter-channel nonlinear interference noise (NLIN). In simulations, we conduct a 30-GBaud 8D-16 quadrature amplitude modulated (8D-16QAM) and conventional polarization division multiplexed quadrature phase shift keying (PDM-QPSK) signals transmission over 2000-km standard single mode fibe (SSMF) in a 5-channel wavelength division multiplexing (WDM) coherent optical communication system. Under the same spectrum efficiency, the 8D-16QAM can obtain a nonlinear gain of more than 0.3dB compared with the conventional PDM-QPSK signal.