A new carrier phase recovery method in faster than Nyquist optical fiber communication system

Faster than Nyquist optical communication system recently attracts more and more attentions because of its higher spectral efficiency than ordinary Nyquist systems. Using a faster than Nyquist signalling, we can compress more than 50 Gbaud symbols in one standard 50 GHz WDM channel. The previous established carrier phase recovery methods which were suitable for ordinary coherent optical communication systems are no longer fit for faster than Nyquist system. In this work, we proposed an optical domain pilot aided carrier phase recovery scheme where the optical pilots are used. The analysis results show a very good performance of high laser linewidth tolerance with very low complexity. We demonstrate that using the proposed scheme the compression factor α, which indicates the scale of inter-symbol interference, can be as small as 0.625 with the achievement of linewidth tolerance of 6×10^-5 with 1 dB OSNR penalty at BER of 1×10^-3.