Properties of proton exchange waveguides in lithium tantalate

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Abstract
The characteristics and properties of proton exchange and annealed proton exchange waveguides in lithium tantalate are investigated. Planar waveguides are first studied using secondary‐ion mass spectrometry (SIMS) to obtain the hydrogen‐ and lithium‐ion concentration profiles. From this data, accurate exchange and anneal diffusion coefficients are calculated. Optical propagation constants are also measured and used in conjunction with the SIMS results to calculate the change in the extraordinary refractive index at λ=0.6328 and 0.829 μm. Infrared‐absorption measurements are also taken to monitor the exchange process. In addition, the surface damage due to proton exchange of the x facet of lithium tantalate is qualitatively investigated. Channel waveguides are also characterized. A parameter space study to determine the fabrication conditions necessary to achieve low‐loss, single‐mode waveguides at λ=0.829 μm is carried out. Mode near‐field sizes and the fiber‐to‐output insertion losses are characterized as a function of anneal time. The polarization extinction ratio and optical damage threshold for typical waveguides are also measured.