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.
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Funding: This work was supported by the U.K. EPSRC Programme
under Grant EP/L000091/1 (PEACE) and Grant EP/S003436/1 (PHOS).
- Optical amplifiers
- nonlinear optics
- optical fiber communication
- phase conjugation