Applied Physics Letters · 1982 · 688 citations · 8 references
Natural SciencesMaterials EngineeringMaterials ScienceOptical MaterialsOpticsPhotonicsDiffusion In SolidsOptical Properties Of SolidsOptical WaveguidesRefractive IndexWaveguidesCrystal OpticsOptical Waveguide MaterialsPolarizationProton Exchange ReactionsWaveguide DesignWaveguide FabricationWaveguide Materials
We describe the fabrication and characterization of optical waveguides formed in LiNbO3 by proton exchange in benzoic acid melts at 200–250 °C. Proton exchange, in LiNbO3 the replacement of lithium ions with protons, takes place when the substrate is immersed in the molten acid. We observe a surface increase in the refractive index of 0.12, for the extraordinary polarization only, with a step function index profile. This is the highest index increase obtainable to date for LiNbO3. Measured diffusion rates for x-cut crystals are 1.37 μm2/h at T = 249 °C and 0.37 μm2/h at T = 217 °C, so that very deep guides can be formed in short times. Diffusion is somewhat slower in the z direction. The process as described is not useful for y-cut crystals, since it damgaes this surface. Losses, measured on x-cut samples, were <0.5 dB/cm. All measurements were made at 0.633 μm.
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