NALM-based, phase-preserving 2R regenerator of high-duty-cycle pulses

Abstract

We explore the potential of the nonlinear amplifying loop mirror (NALM)-based phase-preserving 2R (reamplification and reshaping) regenerator for simultaneous regeneration of multiple wavelength-division-multiplexed (WDM) channels. While not considering nonlinear multi-channel propagation, we address two issues of the phase-preserving NALM that appear to us as the major obstacles in adopting it for realistic WDM applications: a high operating power and a detrimental effect of non-small (33% - 50%) pulse duty cycles. After thorough optimization, we find a new operating regime of this regenerator with the non-small duty-cycle capability and approximately an order of magnitude reduction of the required operating power. In addition, we show that the plateau in the input-output power transfer curve does not automatically lead to the reduction of the amplitude jitter, which is particularly noticeable for the non-small duty-cycle pulses.

All-optical regenerator of multi-channel signals

“…Although, as a proof of concept of GDM-based multi-channel regeneration, the presented experiments have only focused on the Mamyshev regenerator of OOK signals, we believe there is a clear path to extending this GDM approach to more advanced modulation formats in the future. In particular, the GDM nonlinear medium has been predicted to enable a multi-channel phase-preserving amplitude regeneration of phase-encoded signals 49, 50 in a nonlinear amplifying loop mirror (NALM) 51, 52 , which is also capable of regeneration of multiple amplitude levels 53 . The GDM nonlinear medium easily permits bi-directional use, which is essential for NALM operation.…”

Wavelength-dependent nonlinear optical loop mirror for simultaneous amplitude noise reduction at two wavelengths

“…Besides, due to the low dispersion of the loop, there is no substantial walkoff between the channels, so that they do not overlap in the loop. As a consequence, nonlinear interactions between the two channels, in particular through XPM and four-wave mixing, which should be carefully managed in many multiwavelength regeneration schemes [15]- [18], [20], do not occur in this case. If now data occupies all possible time slots, as it happens in most telecom appications, then it is not possible to delay the data at both wavelengths and overlap is unavoidable.…”

“…If now data occupies all possible time slots, as it happens in most telecom appications, then it is not possible to delay the data at both wavelengths and overlap is unavoidable. In this case, careful management of the nonlinear interactions between channels must be implemented, resulting in an increased complexity of the device [20].…”

“…The maximal data rate per channel can be improved by a factor of ∼2 or more if temporal overlap between channels in the loop is allowed. This however will give rise to nonlinear interactions whose mitigation would increase the complexity of the scheme [20]. Finally, spectral broadening sets a limit to the power ratio between channels to be regenerated, as a higher power ratio means larger broadening of the high-power signal, even if the level of the lower-power signal remains nearly constant in each case.…”

“…On the other hand, there is a growing interest to extend the application of the NOLM (and of the related NALM, or nonlinear amplifying loop mirror [19]) towards simultaneous multiwavelength regeneration [20]. In the frame of WDM systems however, where wavelength discrimination is essential, the broadband nature of the NOLM nonlinear response restricts its range of applicability.…”