Continuously Tunable Optical Buffer

现代社会在很大程度上是基于快速可靠的信息交换和处理。这导致了互联网的爆炸式增长，并且每年都增加新的应用和服务，对信息传输容量的需求不断增加-音乐下载正在取代商业街CD购买，仅YouTube上的视频下载量就达到每天30亿次，电视在互联网上直播，高清视频点播即将到来，云计算可能意味着越来越多的数据被远程存储和处理。这些数据中的绝大多数以小数据包的形式通过全球光纤网络传输。目前，网络容量的瓶颈是由路由器形成的，路由器是互联网的“分发中心”，在这里，数据包根据目的地在光纤之间进行交换。这个过程是由电子设备完成的，因此速度比光传输光纤的容量低得多。此外，随着使用接近网络容量限制，路由器处的数据拥塞是一个严重的问题，这需要电子地存储数据分组，直到它们可以被重新传输。最后，从光到电再到光的转换效率也很低，因此会消耗大量的能量。解决这个问题的最有吸引力的解决方案之一是以光的形式存储数据，直到它可以重新传输。这样的光缓冲器应该是快速的，允许任意的存储时间，并且应该是宽带的，也就是说，它应该在用于光纤中的数据传输的整个光波长范围内工作。到目前为止，已经提出了几种光缓冲器，并进行了部分演示，但没有一种能满足所有这些要求。它基于集成光子学，这将最终允许缓冲器进行规模化和大规模制造以供市场使用。在其最简单的形式中，芯片包含两个平行的光波导，其间隔可以电子控制。同时通过两个波导传播的光通过分离的空气间隙光学耦合，并且传播速度取决于该间隙的确切尺寸。换句话说，光的速度以及脉冲在芯片上花费的时间可以通过移动波导来控制。我们已经通过模拟表明，使用这种方法可以将延迟时间改变三倍。因此，在环形配置中使用我们的光缓冲器可以产生任意的时间延迟。此外，预计缓冲器在所有波长的光通信相关的工作。在实际应用中，我们将利用最新的微机电技术在III-V族半导体平台上实现两个波导的可控分离。在本项目中，我们将首先通过理论分析和模拟来设计和优化光缓冲器。然后，我们将使用III-V沉积，电子束光刻，以及等离子体和湿法蚀刻技术的组合来制造该器件。我们会检查和评估这个装置，该项目是南安普顿大学和伦敦大学学院的合作项目，将汇集他们在光子学（UoS）和III-V纳米纤维（UCL）方面的专业知识，研究和制造一种有潜力成为进一步加速分组传输的技术的设备。交换网络，从而用于因特网的未来增长。

Modern society is based to a large extent on the fast and reliable exchange and processing of information. This has led to an explosive growth of the internet, and every year new applications and services are added with ever increasing demands on information transfer capacity - music downloads are replacing high street CD purchases, video downloads have reached 3bn per day on YouTube alone, TV is streamed live on the internet, HD video-on-demand is just round the corner, and cloud computing may mean that data is increasingly stored and processed remotely. The vast majority of these data are transmitted in form of small data packets over a worldwide network of optical fibres. The bottleneck in the capacity is currently formed by the routers, the "distribution centres" of the internet where packets are switched between optical fibres depending on their destination. This process is done by electronics, and thus at much lower speeds than the capacity of the optical transmission fibres. Moreover, as usage nears the network capacity limits, data congestion at the routers is a serious issue which requires storage of data packets electronically until they can be re-transmitted. Finally, the conversion from optical to electronic to optical is also inefficient and thus consumes significant amounts of energy.One of the most attractive solutions to this problem is storing data in its optical form until it can be re-transmitted. Such an optical buffer should be fast, allow for arbitrary storage times, and should be broadband, that is, it should work over the whole range of optical wavelengths used for data transmission in fibres. Several optical buffers have been suggested and partially demonstrated so far, but none of them fulfils all these requirements.Here, we propose a novel type of optical buffer to meet these specifications. It is based on integrated photonics, which will ultimately allow the buffer to be scaled and mass fabricated for the market. In its simplest form, the chip contains two parallel optical waveguides whose separation can be controlled electronically. Light propagating simultaneously through the two waveguides is coupled optically through the separating air gap and the propagation velocity depends on the exact size of that gap. In other words, the speed of light and hence the time the pulse spends on the chip can be controlled by moving the waveguides. We have already shown through simulations that the delay time can be changed by a factor of three using this method. Using our optical buffer in a ring configuration can therefore create any arbitrary time delay. Moreover, the buffer is predicted to work at all wavelengths relevant for optical telecommunications. In practice, the controllable separation of the two waveguides will be achieved using the latest micro-electromechanical technology on a III-V semiconductor platform.In this project, we will first design and optimise the optical buffer by theoretical analysis and simulations. We will then fabricate the device using III-V deposition, e-beam lithography, and a combination of plasma and wet etching techniques. We will characterise and evaluate the device, and finally demonstrate the optical buffer in an optical telecommunication system.The project is a collaboration between the University of Southampton and University College London and will bring together their expertise in photonics (UoS) and III-V nanofabrication (UCL) to investigate and fabricate a device which has the potential to become an enabling technology for further acceleration of packet-switched networks and thus for future growth of the internet.