Matched Filter Design for RRC Spectrally Shaped Nyquist-WDM Systems

We investigate the matched filter design for root-raised-cosine (RRC) spectrally shaped Nyquist wavelength-division-multiplexed (WDM) systems. We show that the complexity of the receiver-side adaptive butterfly equalizer can be significantly reduced by incorporating a matched filter in the static chromatic dispersion equalizer for RRC Nyquist spectrally shaped signals. We find that the Nyquist-WDM system with a matched filter is sensitive to the laser frequency offset between the local oscillator at the receiver and the laser at the transmitter, and show that the frequency offset induced penalty decreases with increased RRC roll-off factor. With a roll-off factor of 0.1, the optical signal-to-noise ratio penalty at BER 10^-3 from 1 GHz frequency offset is for 28-Gbaud polarization division multiplexed quadrature phase shift keying and for 28-Gbaud polarization division multiplexed 16-ary quadrature amplitude modulation.