Multimodal simulations of fibre optical parametric amplifiers and oscillators

Abstract

Systems that are capable of converting light between frequencies are attractive since they can produce output at wavelengths other than those provided by conventional laser sources. These wavelength conversion devices can then be utilised in a variety of applications that require light at unconventional frequencies. Such systems are also useful in the telecommunications industry to convert energy between channels within wavelength division multiplexing fibre systems. Furthermore, since the channels of fibres used within telecommunications are being increased by using multi-mode fibres, mechanisms that can convert energy between these modes are also favourable. To seamlessly apply these converters to the telecommunications fibre network and to maintain the advantages that fibres provide it is preferable for the energy conversions to occur within optical fibres. Fibre optical parametric amplifiers are all-fibre optical systems where the nonlinearity of the materials is utilised for energy conversion between wavelengths and fibre modes. The conversion efficiency of these devices can however be reduced by non-uniformities of parameters along the propagation direction. This adverse effect can though be controlled by enhancing the amplifier system into a fibre optical parametric oscillator. Fibre based amplifiers and oscillators whose purpose is to convert energy between wavelengths and fibre modes are investigated throughout this thesis. The wavelength and mode conversion within these amplifiers and oscillators occurs when light is transmitted through an optical fibre. Pulse propagation through these devices is numerically simulated throughout this study by using the multi-mode generalised nonlinear Schrödinger equation. This model is therefore used to investigate wavelength and mode conversion. Furthermore, the frequency banded generalised nonlinear Schrödinger equation is derived and validated as part of this study. This equation allows the effective and accurate simulation of wavelength conversion over ultra-large bandwidths. Numerical methods that describe the fibre optical parametric amplifiers and oscillators are detailed throughout this thesis. These highly optimised models are then simulated over a multitude of parameters to calculate the efficiency and noise of the parametric systems. Initially, mode conversion using a multi-mode fibre optical parametric amplifier is investigated. Attention is then drawn upon the operation and inner workings of a single-mode fibre optical parametric oscillator. Finally, the research study culminates with the, to the best of the author's knowledge, first investigation into a multi-mode fibre optical parametric oscillator whose purpose is to convert energy between modes.

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ORCID for Peter Horak: orcid.org/0000-0002-8710-8764

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