Fibre Parametric amplifiers for Real Applications in Optical Communication Systems (FPA-ROCS)

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The Fibre Optical Parametric Amplifier (FOPA) has been investigated by many research groups over the preceding thirty-five years as a potential "holy grail" of optical amplification, but has yet to evolve outside of the laboratory. The tantalising prospect of significantly increasing fibre capacity within optical systems by simply and directly employing FOPAs, each with gain bandwidth far exceeding that of the ubiquitous EDFA, has always been historically somewhat offset by a range of challenging physical barriers. Chief amongst these is the innate polarisation sensitivity of the parametric amplification process. This demands that close alignment must be maintained between the polarisation state of an incoming signal and an optical parametric pump which supplies energy to the signal via a nonlinear medium. In a DWDM system, this requirement scales extremely problematically - multiple signals of differing wavelength and in random states of polarisation (often with data carried on both orthogonal modes), must each correlate polarisation-wise with the pump or pumps to receive gain. We believe we have uncovered a ground-breaking new architecture for the FOPA which will ultimately effectively eradicate this significant hurdle, and forms the basis for this proposal's research direction. Other FOPA performance issues must also be overcome. For example, the transfer of intensity noise from the pump to the signals, and the unwanted generation of nonlinear crosstalk within the FOPA via signal-signal interactions are certainly drags on the performance ultimately achievable and will require significant investigation to minimise their effects. However, we do not consider these latter challenges to be such a considerable brick-wall against real-world operation as 'the polarisation question'. FPA-ROCS, is a focused research programme which will provide the required breakthrough to transition the FOPA from problematic laboratory experiment to an amplifier with real potential to impact across the optical communications world. This key advance will be based on our recent first experiments of an innovative FOPA design based on what we are calling the Half Pass Nonlinear Optical Loop or HPL NOL as shown in. We have recently demonstrated the world's first amplification of polarisation-multiplexed DWDM signals using this architecture , and believe it solves several of the large issues highlighted above, most notably offering polarisation independent black-box gain together with exceptional potential for significantly expanded bandwidth beyond the 20nm so far demonstrated. This potential has been outlined by separate characterisation studies undertaken by our team which demonstrated a single polarisation gain bandwidth of >110nm (i.e. 3x greater than that of the EDFA) with a gain variation across the band of only 1dB . We envisage using the HPL NOL to supply gain in regions of the fibre transmission spectrum which are currently untapped, such as at 1300nm (O-band) or 1500nm (S-band). By exploiting new bands in this way, together with considerably wider gain bandwidth per band, the capacity increase offered by FPA-ROCS will be extremely large (>500% current capability) and thus industry and, perhaps, world changing. The technology will be able to operate in parallel with existing optical communications infrastructure due to the transparency of the HPL-NOL outside its gain region (a feature not present in doped fibre amplifiers), enabling co-deployment with field-deployed EDFAs. This will enable a low-cost future upgrade path for network operators without the expensive and environmentally-unfriendly need to lay new fibre as capacity limits are approached. We envisage massively increased data throughputs from our radical redesign of the optical amplifier, allowing fibre systems to be future proofed to some degree at a UK-wide level and beyond.