Enhancement of refractive index in Ti:LiTaO/sub 3/ optical waveguides by Zn vapor diffusion

A double diffusion technique to enhance the effective mode index of optical waveguides in LiTaO/sub 3/ is discussed. It consists of Zn diffusion from the vapor phase at relatively low temperatures (750-800 degrees C), into waveguides initially produced by Ti indiffusion at higher temperature (1150-1200 degrees C). Both X- and Z-cut substrates are investigated. A model combines profiles of both diffusions is formulated to calculate the expected effective index values for planar waveguides. Good agreement is found between experimental results and model predictions which assume that the initial Ti profile is not affected by the lower-temperature Zn diffusion. Effective index enhancements as high as 0.005 and 0.003 are obtained by this method for the fundamental extraordinary and ordinary modes, respectively.<
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