Abstract
One of the main reasons why nonlinear-optical signal processing (regeneration, logic, etc.) has not yet become a practical alternative to electronic processing is that the all-optical elements with nonlinear input–output relationship have remained inherently single-channel devices (just like their electronic counterparts) and, hence, cannot fully utilise the parallel processing potential of optical fibres and amplifiers. The nonlinear input–output transfer function requires strong optical nonlinearity, e.g. self-phase modulation, which, for fundamental reasons, is always accompanied by cross-phase modulation and four-wave mixing. In processing multiple wavelength-division-multiplexing channels, large cross-phase modulation and four-wave mixing crosstalks among the channels destroy signal quality. Here we describe a solution to this problem: an optical signal processor employing a group-delay-managed nonlinear medium where strong self-phase modulation is achieved without such nonlinear crosstalk. We demonstrate, for the first time to our knowledge, simultaneous all-optical regeneration of up to 16 wavelength-division-multiplexing channels by one device. This multi-channel concept can be extended to other nonlinear-optical processing schemes.
Highlights
One of the main reasons why nonlinear-optical signal processing has not yet become a practical alternative to electronic processing is that the all-optical elements with nonlinear input–output relationship have remained inherently single-channel devices and, cannot fully utilise the parallel processing potential of optical fibres and amplifiers
In order to achieve this, we proposed to make an artificial group-delay-managed (GDM) nonlinear medium consisting of a series of short nonlinear fibre sections separated by spectrally periodic phase filters known as periodic group-delay devices (PGDDs)
The presented work consists of two parts: in the first one the regeneration with GDM medium is studied by placing one GDM unit cell consisting of a fibre section and a PGDD into a recirculating loop[23, 24] and letting the signals propagate through this cell multiple times; in the second one we use the obtained insights to build the first stand-alone GDM-enabled Mamyshev regenerator and demonstrate simultaneous regeneration of 16 WDM channels in it
Summary
One of the main reasons why nonlinear-optical signal processing (regeneration, logic, etc.) has not yet become a practical alternative to electronic processing is that the all-optical elements with nonlinear input–output relationship have remained inherently single-channel devices (just like their electronic counterparts) and, cannot fully utilise the parallel processing potential of optical fibres and amplifiers. To be practically viable, one all-optical regenerator must be able to replace a large number of optoelectronic regenerators, which makes its compatibility with WDM the most important challenge[1, 2] This challenge, is of fundamental nature, because the threshold-like input–output power transfer function of a 2R regenerator requires strong optical nonlinearity, which necessarily leads to cross-phase modulation (XPM) and four-wave mixing (FWM) interaction among the WDM channels. The presented work consists of two parts: in the first one the regeneration with GDM medium is studied by placing one GDM unit cell consisting of a fibre section and a PGDD into a recirculating loop[23, 24] and letting the signals propagate through this cell multiple times; in the second one we use the obtained insights to build the first stand-alone GDM-enabled Mamyshev regenerator and demonstrate simultaneous regeneration of 16 WDM channels in it. This paper presents the experiment with optimised dispersion map and Raman amplification, yielding the eye-opening improvements that are significantly greater and more equalised among the channels, and resulting in regeneration of the largest number (16) of WDM channels to date. (While this manuscript was under review, we learned of a more recent work reporting regeneration of 16 channels with 50-GHz spacing, albeit requiring bit synchronisation among all channels: Guan et al.27.) The GDM-based approach can be straightforwardly extended to higher channel counts and higher symbol rates, and we believe it can be adapted for regeneration of more advanced modulation formats
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