Fabrication and characterisation of photorefractive thin films and waveguides

Abstract

This thesis is concerned with the fabrication and characterisation of photorefractive planar waveguides by the techniques of pulsed laser deposition and ion-beam implantation. The formation of photorefractive waveguides is highly desirable for the miniaturisation of optical systems and provides compatibility with other integrated optical devices in current use such as waveguide lasers and optical fibre technology. The optical confinement inherent to waveguides also holds the key to a major speed up in the effective response time of the photorefractive effect. Up to three orders of magnitude decrease is forecast due to the intensity dependence of the photorefractive response time.
This thesis reports the epitaxial growth of thin film optical waveguides of the photorefractive materials Bi₁₂GeO₂₀ and Bi₁₂SiO₂₀ onto heated zirconia substrates by pulsed laser deposition. The epitaxial nature and stoichiometry of the films are verified using x-ray diffraction analysis. Waveguide modes were observed with effective refractive indices in close agreement with theoretical predictions implying that the refractive index of the deposited film is similar to that of the bulk crystal. Pulsed laser deposition has also been used to fabricate waveguides from the chalcogenide glass lanthanum/gallium sulphide. The waveguides demonstrate many characteristic chalcogenide properties such as photo-bleaching, photo-diffusion and a photo-induced change in the refractive index.
Ion-beam implantation has been successfully used to form planar waveguides in the photorefractive materials Bi₁₂SiO₂₀, Sr_xBa_1-xNb₂0₆ and BaTiO₃. The annealing of SBN waveguides and the effect on waveguide propagation loss is discussed. Photorefractive effects have been observed and characterised in BaTiO₃. The expected decrease in the effective photorefractive response time (for a given input power) has been observed, owing to a combination of optical confinement within the waveguide and possible modification of charge-transport properties induced through implantation. Photorefractive two-beam coupling experiments exhibited a decrease in the response time of >10², and an unexpected reversal of the gain direction in the waveguide compared with that of the bulk crystal.

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ORCID for Robert Eason: orcid.org/0000-0001-9704-2204

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