Exceeding the Nonlinear-Shannon Limit using Raman Laser Based Amplification and Optical Phase Conjugation

Abstract

We demonstrate that a combination of Raman laser based amplification and optical phase conjugation enables transmission beyond the nonlinear-Shannon limit. We show nonlinear compensation of 7x114Gbit/s DP-QPSK channels, increasing system reach by 30%.

Signal power asymmetry optimisation for optical phase conjugation using Raman amplification

“…However, the degree of nonlinear compensation using mid-link OPC is related to the asymmetry match of the conjugated and transmitted signal power evolution in the fibre. Meaningful performance improvement has only been demonstrated in Raman-based amplification optical links [4], thanks to the better control over signal asymmetry provided by distributed amplification, as well as its improved noise performance. The key to maximise performance in OPC-assisted systems lies in reducing signal power asymmetry within the periodic spans while ensuring a low impact of noise and non-deterministic nonlinear impairments in the overall transmission link.…”

Enhanced superchannel transmission using phase conjugation

“…Whilst Raman amplification and superchannels are becoming established, the optimum means to compensate nonlinearity is the focus of much research. Candidates include wide-bandwidth digital back propagation 4 , phase conjugate coding 5 and optical phase conjugation (OPC) [6][7][8] . OPC uniquely offers disruption of parametric noise amplification 3 thus overcomes the nonlinear Shannon limit 7 and 60% reach enhancement has been shown for a 1 Tbit/s signal 8 .…”

“…At the output of each OPC, the residual pumps were blocked using thin-film notch filters and the conjugated bands gain-equalised and combined using a second WSS. Unlike previous experiments [6][7][8] this ensured that all channels were launched simultaneously, and that intraband nonlinearity compensation was performed on both bands simultaneously. After propagating through the Raman spans for an identical number of recirculations, a portion of the superchannel under test was filtered using a 20GHz optical filter, detected using a conventional coherent receiver with 26GHz analogue bandwidth and processed using conventional digital signal processing code optimised for Nyquist signals 11 .…”

Detailed characterization of CW- and pulsed-pump four-wave mixing in highly nonlinear fibers

“…For continuous-wave (CW) pumps such OSP includes fiber-optic parametric amplifiers [2] and optical phase conjugation [3,4], whereas broadband pulsed pumps enable e.g. sub-picosecond resolution optical sampling [5] and optical Fourier transformation [Error!…”