Planar integrated optical Bragg grating gas sensors

Abstract

This thesis reports the development and modification of direct ultraviolet (UV) written planar integrated optical Bragg grating refractometers for detection of gases and vapours. The technique of direct UV writing utilises the localised refractive index increase within a UV-photosensitive silica layer, when the layer is exposed to a tightly focussed UV beam, to fabricate a wide range of optical waveguides and optical components. One such component, the Bragg grating, is used as an optical sensor for changes in refractive index.

This thesis reports on the development of practical planar integrated optical Bragg grating gas sensors. This has been achieved through the use of two approaches. The first approach was to increase the number of gas molecules that can interact with the evanescent wave through the use of films of material that extended normally to the surface of the sensor device. Upon functionalisation of a planar Bragg grating sensor device with sol-gel thin films, a response between relative humidity and Bragg wavelength shift was revealed. Functionalisation of the Bragg grating sensor device with a polysiloxane polymer imparted sensitivity to solvent vapours. A quantitative structure-activity relationship (QSAR) approach was used to develop a linear regression model, between Bragg wavelength shift and solvent properties, which had good predicting power.

The second approach was to utilise the associated change in refractive index of a material, when the material changed colour upon exposure to a gas, to create a measurable Bragg wavelength shift. This method was successfully achieved upon interrogation of a Bragg grating sensor device, which had been modified with an encapsulated pH sensitive organic dye upon exposure to hydrogen chloride fumes.

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Identifiers

ORCID for Martin C. Grossel: orcid.org/0000-0001-7469-6854

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