Laser-induced ferroelectric and photonic structures in lithium niobate crystals

Abstract

The influence of laser illumination on ferroelectric domain engineering, waveguide formation and surface micro-structuring in lithium niobate (LN) is investigated. The ability to combine and to manipulate the size and depth of poling inhibited (PI) domains, which are produced by UV-laser irradiation of the +z face of congruent lithium niobate crystals followed by electric field poling, is demonstrated. It is therefore possible to produce complex domain structures, by partially overlapping individual UV laser irradiated tracks thus increasing the utility of this method for the fabrication of surface microstructures. Investigation of the electro-optic performance of ferroelectric/photonic composite structures, which occur naturally as a consequence of the PI process, had shown a significant enhancement (by ~ 36.7 % under the experimental conditions used) of the inherent electro-optic coefficient of the crystal attributed to large range stress at the domain boundaries. The feasibility of UV laser induced PI domain engineering in proton exchanged waveguides in LN was investigated showing that PI domain inversion is in principle possible. It requires however high laser intensity illumination which may produce significant surface damage. Additionally it was found that the proton concentration was also affected by the UV laser irradiation resulting in modifications of the original proton exchanged waveguide structure. Finally, an alternative to UV laser irradiation as a means for PI domain engineering and waveguide formation in LN is presented. This alternative method uses visible c.w. laser irradiation and an amorphous silicon absorbing layer to couple energy into the LN crystal thus emulating the direct absorption that occurs at UV wavelengths.

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ORCID for Sakellaris Mailis: orcid.org/0000-0001-8100-2670

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