This is an online version of my PhD thesis, "Solitons and nonlinear optics in silicon-on-insulator photonic wires". It is also available for download in PDF format.

Abstract

A theoretical study of silicon-on-insulator (SOI) photonic wires was conducted. These nanoscale optical waveguides can have transverse dimensions substantially smaller than the wavelength of the infrared light they carry. This extreme confinement provides very strong dispersion, which can be greatly controlled by specifying the waveguide geometry. The confinement also enhances silicon’s already considerable Kerr nonlinearity (whereby refractive index increases with optical intensity), allowing for nonlinear optical phenomena with record-breakingly small powers.

The most notable of these phenomena (and the prime subject of this report) is the soliton, which is a self-sustaining localised pulse held together by a balance between dispersion and nonlinearity. A variety of other phenomena are also considered, including continuum generation, in which the spectral width of a pulse is greatly increased, and modulational instability, in which deviations from an optical waveform are reinforced by nonlinearity.

Light propagation through a single wire is modelled numerically, and the results compared to third-party experimental data. The analysis reveals that the experimental results are consistent with soliton evolution, thus strengthening the base of evidence for the existence of solitons in silicon wires.

Light propagation through arrays of multiple waveguides is also modelled. It is shown that inter-wire diffraction is intimately linked to dispersion, and that by exploiting this it is possible to realise both solitons and modulational instability in arrays of wires that individually would not be able to support these phenomena. It is also shown that silicon nanowires are an excellent medium for realising "optical bullets" in which a pulse of light is self-localised both in and transverse to the direction of propagation. A distinctive pattern of radiation emitted by these bullets is predicted.

Solitons supported by the Raman effect (rather than the Kerr effect) are also considered. A novel class of soliton solutions are derived, which have the novel property of existing even when the frequency components comprising the soliton are not phase matched.

List of abbreviations

Acknowledgements

I would like to thank my supervisor Dmitry Skryabin for his considerable support and guidance. I would like to thank Andrey Gorbach and Alexey Yulin for patiently answering a great many questions. I would also like to thank my experimental collaborators Richard De-La-Rue, Charles De Nobriga, Wei Ding, Marco Gnan, Jonathan Knight, Marco Sorel and William Wadsworth for the opportunity to turn theory into experimental reality.

Declaration of work previously published and work done in conjuction with others

• Figures 1.2, 3.15, 3.16 and 3.17 incorporate third-party experimental data as credited.
• Figures 3.16, 3.17, 3.18 and 3.19 of which I am the creator (excepting the inclusion of third-party experimental data as credited) have been published elsewhere. (Optics Express, 16:3310, 2008.)
• Figures 4.2, 4.3, 4.4, 4.9, 4.13, 4.16, 4.18 and 4.19, of which I am the creator, have been published in whole or in part elsewhere. (Optics Express 17:5879, 2009.)
• Figures 5.2, 5.3, 5.5, 5.6, 5.7, 5.8, 5.9, 5.10, 5.11, 5.12, 5.17, 5.18, 5.21, 5.22 and 5.23, of which I am the creator, have been published in whole or in part elsewhere. (Physical Review A, 78:033818, 2008.)

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