All-Optical Signal Processes Enhanced by Multi-Mode Nonlinearities

光通信网络正在经历一场重大变革，适应每秒多太比特的通信流量，使用具有更多单个波长载波的快速低延迟解决方案，同时提高能源效率。与此同时，光网络接近饱和，世界各地的研究小组正在积极探索新的传输技术，以满足不断增长的数据流量的需求。在这种变化的环境中，迫切需要开发出比广泛采用的固定带宽掺铒光纤放大器具有更宽带宽（和数据容量）的新型光放大器。模分复用作为一种在少模光纤上支持每波长多模信道的方法被提出并进行了研究。利用模分复用的基本原理，在这个博士项目中，利用少模光纤的不同模式，通过参数化四波混频，利用光纤中的三阶非线性光效应，提供宽带光放大和波长转换。相对于单模系统，这种方法在四波混频系统的工程设计中提供了额外的自由度，这源于剪裁不同光纤模式的传播特性。这个高度实验性的博士项目研究光纤几何形状和实验配置，这将允许在宽波长范围内发生参数效应。本项目首先比较研究了模内和模间四波混频。然后着重于极化效应，并研究所讨论的非线性过程的极化依赖性。此外，利用少模光纤的色散特性，可以观察宽带波长转换，或者相反，在感兴趣的波长中观察非常局部化的参数增益。

Optical communication networks are undergoing a major transformation, accommodating multi- terabit per second communication traffic, using fast and low-latency solutions with even more individual wavelength carriers, all the while improving energy efficiency. At the same time, optical networks approach saturation, and novel transmission techniques that will satisfy the demand for an ever-increasing data traffic are actively being explored by research groups worldwide. In this transforming environment, there is an urgent need for the development of novel optical amplifiers that will exhibit substantially broader bandwidth (and data capacity) than the widely-adopted erbium doped fibre amplifier with fixed bandwidth.Mode-division multiplexing has been proposed and studied as a means of supporting multiple modal channels per wavelength on a few-mode fibre. Using the basic principles of mode-division multiplexing, in this PhD project, the different modes of few-mode fibres are being utilised as a means of providing broadband optical amplification and wavelength conversion through parametric four-wave mixing that exploit third-order nonlinear optical effects in the fibre. Relative to single-mode systems, this approach offers an additional degree of freedom in the engineering of the four-wave mixing system, which originates from tailoring the propagation characteristics of the different fibre modes. This highly experimental PhD project studies the fibre geometries and experimental configurations that will allow the onset of parametric effects over a wide wavelength range. The project starts with a comparative study between intra- and inter-modal four wave mixing. It then focuses on polarisation effects and studies the polarisation dependence of the nonlinear processes in question. Furthermore, the dispersion characteristics of few-mode fibres are exploited in order to either observe broadband wavelength conversion or conversely, very localised parametric gain in the wavelengths of interest.