Annealed proton-exchanged z-cut LiTaO3 planar waveguides fabricated with pyrophosphoric acid have been characterized. For proton exchange, the extraordinary index increase Δ ne ranged from 0.0119 to 0.0141, depending on the exchange temperature. The effective diffusion coefficient De 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 Δ ne and a lower propagation loss. For proton exchange in lithium phosphate-diluted pyrophosphoric acid, a lower Δ ne was obtained, but De 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 ns were measured at regular intervals. Figures and empirical formulas relating the waveguide depth d and the surface index increase Δ ns 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 Δ ns, 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
Dennis Kan and Gar Lam Yip, "Planar LiTaO3 waveguides fabricated by proton exchange in concentrated and diluted pyrophosphoric acid with annealing," Appl. Opt. 35, 5348-5356 (1996)