All-Optical Signal Processes Enhanced by Multi-Mode Nonlinearities

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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.