Abstract

Annealed proton-exchanged z-cut LiTaO₃ planar waveguides fabricated with pyrophosphoric acid have been characterized. For proton exchange, the extraordinary index increase Δn_e ranged from 0.0119 to 0.0141, depending on the exchange temperature. The effective diffusion coefficient D_e ranged from 0.1325 μm²/h at 240 °C to 0.545 μm²/h at 280 °C. Single-mode propagation losses were α = 0.7 dB/cm. Compared with benzoic acid, pyrophosphoric acid produces waveguides with a higher Δn_e and a lower propagation loss. For proton exchange in lithium phosphate-diluted pyrophosphoric acid, a lower Δn_e was obtained, but D_e and propagation losses were not reduced. After proton exchange, the waveguides were annealed. The surface index initially increased, peaked, and then decreased. The waveguide depth d and the surface index n_s were measured at regular intervals. Figures and empirical formulas relating the waveguide depth d and the surface index increase Δn_s to the anneal time, anneal temperatures, and the waveguide depth after proton exchange are given. An example is given in which, the desired waveguide parameters d and Δn_s, the fabrication conditions could be calculated with the previously derived formulas. Propagation losses decreased to 0.4 dB/cm after prolonged annealing.

© 1996 Optical Society of America

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