Combating Fiber Nonlinearity Using Dual-Order Raman Amplification and OPC

We experimentally demonstrate, for the first time, a significant 34-dB nonlinear product power compensation in a mid-link optical phase conjugation (OPC) system using an optimized dual-order distributed Raman amplification (DRA) technique. The dual-order backward (BW)-pumping scheme shows a record signal power symmetry of 97% over 50.4-km single-mode fiber (SMF) spans. We also demonstrate that the required accuracy for span-to-span power alignment is within ±1 dB in order to maintain 20-dB nonlinear product compensation. For a 256-Gb/s dual-polarization-16 QAM transmission over 100.8 km (2 × 50.4 km) SMF with mid-link OPC, the proposed Raman amplification scheme enables the OPC to improve the nonlinear threshold by ~7 dB and the optimum signal launch power by ~5 dB compared with the system without OPC.