Effective suppression of nonlinear distortion in optical phase conjugation of optical OFDM signals using backward Raman pumping

Abstract

ABSTRACTThe use of backward Raman amplification to mitigate nonlinear distortion in optical phase conjugation (OPC) of orthogonal frequency-division multiplexing (OFDM) signals in a fibre communication system is investigated in this paper. A ∼29 dB reduction in the nonlinear distortion is achieved, while comparable conjugated output signal power is maintained through the Raman gain. By numerically solving the nonlinear Schrodinger equation (NLSE) along the fibre, a detailed theoretical model is developed to elaborate the mechanism in Raman-assisted OPC. Different optical network scenarios have been analysed using this model. The mechanism of Raman-assisted OPC is further explained by comparing the power profiles of both the conjugated signal and the nonlinear distortion with those in the conventional scheme. In addition to investigating the nonlinear distortion caused by spurious four-wave mixing (FWM) products, the waveform distortion resulting from pump depletion in the OPC system is also analysed. The ...