In this work, we report on an investigation of the ytterbium diffusion characteristics in lithium niobate. Ytterbium-doped substrates were prepared by in-diffusion of thin metallic layers coated onto x- and z-cut congruent substrates at different temperatures. The ytterbium profiles were investigated in detail by means of secondary neutral mass spectroscopy, optical microscopy, and optical spectroscopy. Diffusion from an infinite source was used to determine the solubility limit of ytterbium in lithium niobate as a function of temperature. The derived diffusion parameters are of importance for the development of active waveguide devices in ytterbium-doped lithium niobate.
We report on fabrication of ridge waveguides formed in congruent periodically poled lithium niobate substrates using annealed and reverse proton exchange followed by diamond blade dicing. 1 W of second-harmonic generation at 775 nm has been obtained in a single-pass in 50 mm long ridge waveguides with internal conversion efficiency of 70%. At this power level, 97% pump depletion has been reached. Although elevated temperature operation and ridge geometry help to mitigate photorefractive damage (PRD) effects, nevertheless, at even higher second harmonic outputs significant power drop with blue shift and distortion of the SHG tuning curve have been observed indicating an onset of PRD.
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