Investigation of crosstalk suppression techniques for multi-wavelength regeneration based on data-pump FWM

Abstract

Multi-wavelength regenerators free of inter-channel crosstalk are desirable for wavelength-division-multiplexing systems from the cost-effectiveness point of view. Three crosstalk suppression methods, including polarization multiplexing, time interleaving and bidirectional transmission, are experimentally investigated in a data-pump four-wave mixing (FWM)-based dual-wavelength regeneration system. The results show that: (1) polarization multiplexing can suppress inter-channel degenerate FWM, but it cannot suppress the non-degenerate FWM unless the fiber has a sufficiently high birefringence; (2) the optimal relative delay time is half a bit period for input signals with 50% duty cycle in the time-interleaving system; (3) in the bidirectional system, if the regenerated signal and the opposite input signal have the same wavelength, the influence of the scattering wave should be considered. Furthermore, an eight-wavelength regeneration scheme is put forward and the inter-modulation characteristics of the regenerated channels are calculated from the nonlinear coupled-mode equations. The Q factor of each regenerated channel can be more than doubled when the duty cycle is 0.2 and the fiber DGD is 40ps/km.