All-optical 2R regeneration of multi-channel WDM signals

All-optical regeneration is one of the key enablers of future transparent optical networks. However, the advance of this technology into practical communication systems has been hindered by its apparent incompatibility with WDM: all-optical regeneration relies on large amount of intra-channel optical nonlinearity, which is always accompanied by debilitating four-wave-mixing (FWM) and cross-phase-modulation (XPM) interactions among the channels, which prohibit WDM operation. The talk will present the recent work of Prof. M. Vasilyev's group on solving this fundamental problem by developing 2R regenerators scalable to large WDM channel counts (done in collaboration with Prof. T. I. Lakoba from the University of Vermont). The key element in our approach is a novel nonlinear medium with a special dispersion map that is both spatially- and spectrally-periodic (we call it a group-delay-managed, or GDM, medium to distinguish it from conventional dispersion-managed links). In the lab, we build it from short pieces of highly-dispersive highly nonlinear fiber, separated by phase filters with periodic saw-tooth-like group-delay spectra, so that the group-delay spectrum of each fiber-filter unit section looks like a staircase. Hence, in GDM medium, different WDM channels propagate with very different group velocities (which suppresses FWM and XPM), whereas various frequency components of the same channel travel with the same velocity, preserving the pulse integrity and ensuring accumulation of self-phase-modulation (SPM). The talk will discuss our experimental results demonstrating the GDM-enabled simultaneous regeneration of up to 12 WDM channels (at 10 Gb/s each) in Mamyshev 2R regenerator based on SPM spectral broadening followed by offset bandpass filtering. With 200-GHz channel spacing required to accommodate spectral broadening in the Mamyshev scheme, we have observed no inter-channel penalties. A discussion of the potential ways in which the novel GDM medium can benefit other 2R regenerator types, different spectral efficiencies, bit rates and modulation formats will conclude the presentation.