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Kumar, Das Soumitra (2019) The finite operator model for step index fibres. PhD thesis, University of Nottingham.

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Abstract

A ray-based dynamical model is developed to propagate light in passive optical fibres. The developed model provides an efficient way to investigate light propagation in the presence of boundary deformations in optical fibre waveguides using concepts of ray billiards and wave-chaos theory. The light propagation is modelled using the phase space transport, where the phase space method is a standard tool of tracing rays in enclosed cross-sectional boundaries. In the developed model, the light propagation is achieved using coarse-grained phase spaces and Ulam's method is adopted for the numerical discretisation. The phase space is divided into rectangular regions or pixels, and a bundle of rays are traced as ensembles from one pixel to the next. The coarse-graining transforms the process of tracing individual light trajectories into a probabilistic way of mapping power from one region of the phase space to another. On this basis, a finite operator model, a form of Frobenius-Perron operator, is developed to propagate light in 3D fibres. The finite operator deterministically distributes power in the pixelated phase space.

The aim of this work is to investigate chaotic and regular ray propagation deformed optical fibres primarily for applications in mid-infrared (MIR) photonics using MIR transparent glasses. However, the model developed here is generally applicable to any deformed unstructured and step-index fibres. The finite operator method enables the calculation of the net accumulation of power in the core in the step index fibres due to the propagation of any arbitrary input light distributions. Using the model, it is possible to investigate the variation of the accumulated power in the core with the variations in any structural deformations of the fibre, variations in the refractive indices of core and cladding media, and the variations in any input light distribution. The study sheds light on ways in which pump power absorption in rare-earth (RE) doped active fibres can be improved. In this thesis, the investigation is carried out to find ways of improving the captured power in an undoped core in passive fibres, and the variations in the propagation mechanisms are characterised from a given input light distribution by varying the structural features of the step index fibre. On the basis of the results, the future extension of the method to study pump power absorption in active fibres is briefly discussed. The finite operator method overcomes previous limitations of light propagation models in asymmetric optical fibres.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Benson, T.M. Creagh, S.C. Sujecki, S.
Keywords:	light propagation; optical fibres; deformed step index fibres
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) > TA1501 Applied optics. Phonics
Faculties/Schools:	UK Campuses > Faculty of Engineering
Item ID:	56266
Depositing User:	Kumar, Das
Date Deposited:	18 Jul 2019 04:40
Last Modified:	07 May 2020 12:01
URI:	https://eprints.nottingham.ac.uk/id/eprint/56266

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