Suppression Mechanism and Optimization of Nonlinear Effects of High-Order Raman Amplification in Ultra-Long-Haul Optical Transmission Systems

To solve the problem of nonlinear effect accumulation in ultra long distance optical transmission system, a collaborative nonlinear suppression architecture based on high-order Raman amplification is proposed in this paper. Specifically, it employs a three-pronged innovative approach: first, implementing a fourth-order pump scheme for multi-band (C+L) gain equalization; second, introducing segmented adaptive dispersion spectrum optimization to dynamically configure dispersion compensation modules, creating a “nonlinear anti-gradient”; and third, incorporating a feedback-based phase conjugate modulation mechanism embedded within the pump path to compensate for Kerr-induced phase distortion. Experimental results demonstrate significant improvements: gain flatness in C+L band was enhanced (peak-to-peak fluctuation reduced from 4.3 dB to 0.9 dB), the nonlinear threshold power increased by 2.5 dB (from 3.0 dBm to 5.5 dBm over 5000 km), and Kerr phase drift was effectively suppressed (reduced from 0.52 rad to 0.28 rad at 8 dBm input power), confirming the efficacy of the synergistic strategy in suppressing nonlinear impairments for enhanced ultra-longhaul transmission.