Stokes, N. A. D.; (1990) Fibre-optic microresonators and sensor systems. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is concerned with the theoretical and experimental investigation of fibre-optic microresonators and sensor systems. Fibre-optic microresonators combine the advantages of resonator sensors and fibre-optics by using microfabricated silicon-based vibrating elements. First the methods of microresonator fabrication are outlined, and a number of devices which have been fabricated in-house are described. Some significant features, which are expected to effect device performance, are also identified. The resonant behaviour of the microbeams is considered. Their response under the influence of a modulated exciting optical beam from a fibre-optic link is derived, and fabrication-induced effects are analysed. A two-source fibre-optic system is developed and the devices examined experimentally using this system. The response of both metal-coated silicon dioxide and metal-coated silicon microresonators is compared with the predicted behaviour. The theory of the temperature and pressure dependences of the resonance frequencies of microresonator beams is developed. The effects of applied pressure and of a change in temperature on both metal-coated silicon dioxide and metal-coated silicon devices are examined using the two-source fibre-optic system. These experimental results are compared with the predictions and conclusions drawn regarding the suitability of the devices for different sensing applications. A fibre-optic system for the activation and detection of the microresonator vibrations incorporating a single, unmodulated optical source is proposed. A possible mechanism for self-excitation of microbeams is described, and conditions for sustaining these vibrations are defined. Self-excitation of microbeams is demonstrated using such a system. The temperature variation of resonance frequency of a self-excited microresonator is measured, and two self-excited devices are multiplexed on a single-source fibre-optic system.

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