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年里已经被许多研究小组作为光学放大的潜在“圣杯”进行了研究，但尚未在实验室之外发展。通过简单而直接地使用fopa（每个fopa的增益带宽远远超过无处不在的EDFA），在光学系统中显着增加光纤容量的诱人前景一直在历史上被一系列具有挑战性的物理障碍所抵消。其中最主要的是固有的极化灵敏度的参数放大过程。这就要求必须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参量泵浦之间保持紧密的对准。在DWDM系统中，这一要求的缩放非常有问题——不同波长的多个信号和随机偏振状态（通常是两个正交模式的数据），必须每个信号都与泵浦或泵浦的偏振相关才能接收增益。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，并为本提案的研究方向奠定基础。其他FOPA性能问题也必须克服。例如，从泵到信号的强度噪声的传递，以及通过信号-信号相互作用在FOPA内产生的不必要的非线性串扰肯定会影响最终实现的性能，并且需要进行重要的研究以尽量减少它们的影响。然而，我们并不认为后一种挑战会像“两极分化问题”那样，成为对抗现实世界运作的巨大障碍。FOPA - rocs是一个重点研究项目，它将提供所需的突破，使FOPA从有问题的实验室实验转变为具有真正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的创新FOPA设计的第一次实验，该实验基于我们称之为半通非线性光环路或HPL NOL，如图所示。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信号的放大，并相信它解决了上面强调的几个大问题，最值得注意的是提供了偏振无关的黑箱增益，以及迄今为止所展示的显著扩展带宽超过20nm的非凡潜力。我们团队进行的单独表征研究概述了这种潜力，该研究表明，单极化增益带宽为bb10 110nm（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在目前尚未开发的光纤传输频谱区域提供增益，例如1300nm （o波段）或1500nm （s波段）。通过以这种方式开发新频段，加上每个频段相当宽的增益带宽，FPA-ROCS提供的容量增加将非常大（bbb500%的当前能力），从而改变行业，甚至可能改变世界。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（掺杂光纤放大器不具备这一特性），能够与现场部署的edfa共同部署。这将为网络运营商提供一种低成本的未来升级路径，而无需在接近容量限制时铺设昂贵且不环保的新光纤。我们设想通过对光放大器的彻底重新设计，大量增加数据吞吐量，使光纤系统在某种程度上在英国范围内甚至更远的地方得到未来的证明。

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.