Direct UV writing of structures in lithium niobate and lithium tantalate

Abstract

This thesis presents results from fabrication of UV direct write structures in lithium niobate and lithium tantalate. Unassisted direct writing of surface channel waveguides using lambda = 244 nm cw light resulted in polarisation specific waveguides fabricated on z- cut crystals. Waveguides were characterised using mode profiles, propagation losses, numerical aperture and refractive index measurements. In z-cut congruent lithium niobate, waveguides were written on the +z and -z faces producing structures that guided TM polarisation only with +z face waveguides exhibiting the lowest propagation loss of ~ 2 dB/cm, a maximum refractive index difference of ~ 8 x 10^-4 and a mean lifetime tau of ~ 4.5 days. The waveguiding mechanism is believed to be due to a lithium out-diffusion enhanced by a transient photorefractive effect. Waveguides were also written in stoichiometric and doped samples to test improvements in waveguide lifetimes. Surface domain reversal was observed in congruent lithium niobate on both +z and -z faces. Channel waveguides written into lithium tantalate were characterised and compared with lithium niobate.

Surface ferroelectric domain reversal via illumination of single pulsed lambda = 266 nm light through a phasemask on +z face congruent lithium niobate produced ordered alignment of domain lines along the crystallographic y-axes with minimum domain separation width of ~ 2 μm. Results from high temperature exposures and multipulse regimes are presented and a domain formation mechanism is proposed via an Nb anti-site model.

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

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