Photorefractive damage thresholds in Zn- and Zr-doped thin-film lithium niobate

We report a systematic study of photorefractive damage resistance in undoped, Zn-doped, and Zr-doped thin-film lithium niobate (TFLN) at visible and near-infrared wavelengths. Zn2+ or Zr4+ ions were incorporated into congruent z-cut LiNbO3 wafers via high-temperature in-diffusion, resulting in surface concentrations of 4.0 and 1.1 mol. %, respectively. TFLN-on-insulator was then fabricated from these wafers using wafer bonding and crystal ion slicing. Photorefractive damage (PRD) thresholds in 600 nm thick planar waveguides were determined through in-plane scattering of a prism-coupled laser beam, complemented by transmittance measurements. Incorporation of Zn and Zr was found to enhance the PRD resistance by up to two orders of magnitude compared to undoped TFLN within the investigated wavelength range. For comparison purposes with the planar waveguides, PRD thresholds in two-dimensional rib waveguides, etched in an undoped TFLN substrate, were measured.