Abstract

Nyquist WDM systems generally use non-adaptive digital filters with sharp cut-off characteristics to extract the target wavelength signal. Unfortunately, wavelength division demultiplexing (WDD) using non-adaptive filters suffers degraded signal quality under frequency offset and receiver IQ impairments. When the signal to be detected suffers frequency offset, the target channel spectrum deviates from the passband frequency of the non-adaptive filter. This signal then experiences inter-symbol interference and inter-channel crosstalk in the WDD process. In addition, both inter-channel crosstalk and intra-channel crosstalk are caused by the interaction between frequency offset and receiver IQ impairments. This paper elucidates, for Nyquist WDM systems, this interaction in the WDD process and proposes a digital coherent receiver robust against such interactive impairments. Simulations show the feasibility of the proposed digital coherent receiver. Its effectiveness is validated through experiments on 32 Gbaud dual-polarization 16 quadrature amplitude modulation signals with 33 GHz channel spacing.