Optical Properties of Silicon-On-Insulator Waveguide Arrays and Cavities

  • Gareth Hobbs

Student thesis: Doctoral ThesisPhD


This thesis details work undertaken over the past three and a half years looking at the optical properties of silicon-on-insulator waveguide arrays and 1D photonic crystal microcavities. Chapter 1 contains relevant background information, while chapters 2, 3 and 4 contain results of experimental work. Chapter 5 summarises the results and conclusions of the preceding chapters and also suggests some directions for possible future research. Chapter 1 starts by introducing some of the fundamental aspects of guided wave optics and how these relate to silicon-on-insulator waveguides. The modes of single,uncoupled silicon waveguides are described, along with a brief description of how such waveguides can be fabricated. Following this a short introduction to optical cavities and the relevant parameters that can be used to describe them is provided. In Chapter 2 results are presented that experimentally confirm the presence of couplinginduced dispersion in an array consisting of two strongly-coupled silicon-on-insulator waveguides. This provides an additional mechanism to tailor dispersion and shows that it is possible to achieve anomalous dispersion at wavelengths where the dispersion of a single wire would be normal. In Chapter 3 the focus switches to the linear properties of 1D photonic crystal microcavities in silicon. The optical transmission of a number of different devices are examined allowing the identification of suitable microcavities for use in nonlinear measurements. Microcavities with Q-factors in excess of ∼40,000 were selected for use in the work presented in Chapter 4, whilst the possibility of thermally tuning the microcavity resonances is also investigated. A cavity resonance shift of 0.0770± 0.0004 nm K-1 is measured experimentally. Chapter 4 looks at the nonlinear transmission of those microcavities identified as suitable in Chapter 3. More specifically, the response of the microcavities to thermal and free carrier induced bistability is considered. Thermally induced bistability is observed at a threshold power of 240 μW for the particular cavity chosen, with a thermal time of 0.6 μs also measured. Free carrier induced bistability is then observed for pulses with nanosecond durations and milliwatt peak powers. Following that, the interplay of thermal and free carrier effects is observed using input pulses of a suitable duration.
Date of Award9 Dec 2014
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorWilliam Wadsworth (Supervisor)


  • silicon-on-insulator
  • photonics
  • waveguides
  • microcavities

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