Microstructuring and domain-engineering of lithium niobate using combinations of light, etching and poling

Abstract

The work presented in this thesis reports methods for microstructuring of lithium niobate. The process of light induced frustrating etching, where light from a laser is used to inhibit the etching of iron doped lithium niobate, is the subject of a detailed investigation so a better understanding of the process can be developed. The process was found to be dependent upon illumination and etch times, iron dopant levels, and irradiance levels. Analysis of the structures formed revealed that they were resistant to the etchant used and were positively charged. Two dimensional Fourier transform analysis of images obtained were used to confirm that the structures preferentially propagated along 3 directions each 120º apart.

A novel electro-optically controlled domain-engineered total internal reflection switch and beam deflector is also reported. Device construction uses electric field poling of lithium niobate to create two parallel but oppositely oriented domains. When an electric field is applied across the interface between these domains a change in the refractive index of equal magnitude but of opposite sign is induced. If light incident on this interface sees a sufficient difference in refractive index it can be total internally reflected. The total internal reflection switch shows high contrast ratio switching of greater than 20dB and is less wavelength dependent than other electro-optic switches, such as the Pockels cell. The beam deflector can produce large angular deflections, which are increased by faceting of the output face. Deflections of greater than 18o have been demonstrated using this technique. Cascading of devices and possible device implementations are also suggested.

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

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