Pilot-added carrier-phase recovery scheme for Nyquist M-ary quadrature amplitude modulation optical fiber communication system

A new two-stage carrier-phase recovery scheme using a combination of an optical pilot-aided algorithm with the crossed constellation transformation algorithm for either square-framed or non-square-framed M-levelquadrature amplitude modulation(QAM) Nyquist systems is proposed.It is verified in 32-and 128-QAM systems that it can provide high linewidth tolerance with little complexity.