Advanced all-optical signal processing using quadratic nonlinearities

随着互联网的出现，数据业务已经迅速取代语音成为当今高速光通信网络传输的主要信息类型。此外，在电子邮件、电子商务和视频会议等现有应用沿着远程医疗、虚拟现实游戏和视频点播等新兴应用的推动下，预计在可预见的未来，通信量将继续以惊人的速度增长。为了增加光网络的能力和灵活性以允许新的服务和下一代互联网，在光层内处理数据信号将变得越来越有吸引力，如果不是必需的话。因此，这些先进电信网络的节点将需要能够以极高的速度（40 Gbit/s及以上）并行无缝处理多个信号的高功能光学设备。因此，需要在电气系统中使用的调制器、开关和混频器的光学模拟物，指示需要使用非线性光学效应。到目前为止，对非线性光学器件的大部分研究集中在使用具有超快但不幸的是固有低非线性的光纤或遭受相对低的开关速度的半导体材料。在这个项目中，我们建议调查一种不同的方法，基于使用二次非线性，尽管他们有许多有吸引力的属性，仍然是最少探索的选择，在电信领域。为了证明和利用二次非线性在这一领域的全部潜力，我们希望设计和开发几个紧凑的，二次全光处理模块能够在适度的光功率水平，并能够满足严格的要求，大容量电信系统。为了实现这一点，我们将利用级联的非线性效应在周期性极化的锂酸盐波导。我们还将寻求利用各种脉冲整形技术，并使用新颖的切趾非线性光栅设计。应该理解的是，虽然电信是本项目中要考虑的主要目标应用，但开发的几个器件概念也应该用于计量学、光谱学、传感、生物学和医学等领域的其他全光处理应用。

With the advent of the Internet data traffic has rapidly over taken voice to become the dominant type of information transported by today's high speed optical communication networks. Moreover traffic is predicted to continue to grow at a phenomenal pace for the foreseeable future, driven by existing applications such as e-mail, e-commerce and video conferencing along with emerging applications such as telemedicine, virtual reality games and video-on-demand. In order to increase the capability and flexibility of optical networks to allow for new services and the next generation Internet, it will become increasingly more attractive, if not essential, to process the data signals within the optical layer. The nodes of these advanced telecom networks will thus require highly functional optical devices capable of seamlessly processing multiple signals in parallel at extremely high speeds (40 Gbit/s and beyond). The optical analogues of the modulators, switches and mixers used in electrical systems are thus required, dictating the need to use nonlinear optical effects.To date the majority of research into nonlinear optical devices has focussed on the use of optical fibre which posseses an ultrafast but unfortunately inherently low nonlinearity, or semiconductor materials which suffer from relatively low switching speeds. In this project we propose to investigate a different approach, based on the use of quadratic nonlinearities, which despite their many attractive properties, still remain the least explored option in the telecom area. To prove and leverage the full potential of quadratic nonlinearities in this field, we want to design and develop several compact, quadratic all-optical processing modules capable of operating at modest optical power levels and that are able to meet the stringent requirements of ultrahigh capacity telecom systems. To achieve this we will exploit the use of cascaded nonlinear effects in periodically poled lithium niobate waveguides. We shall also look to exploit various pulse shaping techniques, and the use of novel apodised nonlinear grating designs. It is to be appreciated that although telecoms is the main target-application to be considered within this project several of the device concepts developed should also be of use for other all-optical processing applications in fields such as metrology, spectroscopy, sensing, biology and medicine.