Multi-tone counter dithering of terabit/s polarization multiplexed signals for enhanced FWM with a single pump

We demonstrate low-noise degenerate four-wave mixing (FWM) of a 24×100Gb/s DP-QPSK signal with a high 50% conversion-efficiency, enabled by counter-phase modulating it and a CW pump at two frequencies. An improved signal Q²-factor by an average of 5.3 dB is achieved.

Introduction

Low noise degenerate four-wave mixing (FWM) with a single pump has promising applications for optical signal processing over broad bandwidths^1–4. Applying it to more advanced dual polarization multiplexed (DP) signal format has been shown using polarization insensitive FWM, enabled by bi-directional propagation of the signal and pump in a loop of highly nonlinear optical fibre (HNLF)^1–4. Despite the scheme's good performance in general, the maximum FWM power conversion efficiency (CE) from the signal to the idler frequency is usually lower compared to non-degenerate FWM in straight line HNLF with 2 orthogonally polarized pumps⁵.