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

光纤参量放大器（FOPA）在过去的35年里被许多研究小组作为光放大的潜在“圣杯”进行了研究，但尚未在实验室之外发展。通过简单直接地采用FOPA（每个FOPA的增益带宽远远超过普遍存在的EDFA的增益带宽）来显著增加光学系统内的光纤容量的诱人前景在历史上总是被一系列具有挑战性的物理障碍所抵消。其中最主要的是参数放大过程的固有偏振敏感性。这就要求在输入信号的偏振态和通过非线性介质向信号提供能量的光学参量泵浦之间必须保持紧密对准。在DWDM系统中，这一要求的缩放非常成问题-不同波长和随机偏振状态的多个信号（通常在两个正交模式上携带数据）必须各自与泵浦或泵浦进行偏振相关以接收增益。我们相信，我们已经为FOPA发现了一个突破性的新架构，它将最终有效地消除这一重大障碍，并构成本提案研究方向的基础。还必须克服FOPA的其他性能问题。例如，从泵浦到信号的强度噪声的转移，以及FOPA内经由信号-信号交互的非线性串扰的不希望的生成，肯定会拖累最终可实现的性能，并且将需要大量的研究来最小化它们的影响。然而，我们并不认为这些挑战是对现实世界的操作作为“两极分化问题”这样一个相当大的砖墙。FPA-ROCS是一项重点研究计划，将提供所需的突破，将FOPA从有问题的实验室实验转变为具有真实的潜力影响整个光通信世界的放大器。这一关键进展将基于我们最近首次进行的创新FOPA设计实验，该实验基于我们所称的半通非线性光学环路或HPL NOL，如所示。我们最近展示了世界上第一个使用这种架构的偏振复用DWDM信号放大器，并相信它解决了上述几个大问题，最值得注意的是提供了偏振无关的黑盒增益，以及迄今为止展示的20 nm以上的显著扩展带宽的特殊潜力。我们的团队进行的单独特性研究已经概述了这种潜力，该研究表明，单偏振增益带宽> 110 nm（即比EDFA大3倍），整个频带的增益变化仅为1dB。我们设想使用HPL NOL在光纤传输光谱的当前未开发的区域中提供增益，例如在1300 nm（O波段）或1500 nm（S波段）。通过以这种方式利用新的频带，以及每个频带相当宽的增益带宽，FPA-ROCS提供的容量增加将非常大（>500%当前容量），从而改变行业，甚至改变世界。该技术将能够与现有的光通信基础设施并行运行，因为HPL-NOL在其增益区域之外具有透明性（掺杂光纤放大器中不存在的功能），从而能够与现场部署的EDFA共同部署。这将为网络运营商提供低成本的未来升级路径，而无需在接近容量限制时铺设新光纤，成本高昂且对环境不友好。我们设想通过对光放大器的彻底重新设计来大幅增加数据吞吐量，从而使光纤系统在一定程度上在英国乃至更高的水平上得到未来的验证。

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.