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Improving the Nonlinear Tolerance of Fiber-Based Optical Phase Conjugation

We demonstrate the use of Raman amplification to mitigate nonlinear distortion in optical phase conjugation (OPC) for a coherent optical orthogonal frequency-division multiplexing system. The OPC distortion is suppressed by lowering the input signal power. Meanwhile, the back-propagating Raman pump enhances the conversion efficiency, thus maintaining a comparable conjugated output signal power. The improvement in OPC signal quality by the Raman pump is numerically solved. Experimentally, the optimized output power can be enhanced by 10 dB and the maximum quality is improved by 1.2 dB. The input power dynamic range is also extended by up to 7 dB. This scheme is potentially applicable in mitigating the crosstalk among multichannel signals in a wavelength division multiplexing system.