Investigation of design options for overlaying 40Gb/s coherent PDM-QPSK channels over a 10Gb/s system infrastructure

To contain limitations from cross nonlinear effects caused by 10Gb/s NRZ channels onto 40Gb/s coherent polarisation division multiplexing quadrature phase shift keying (PDM-QPSK) channels, we investigate the benefits of optimizing the carrier phase estimation process and introducing band-gaps in the multiplex.