Annealed proton-exchanged z-cut LiTaO3 planar waveguides fabricated with pyrophosphoric acid have been characterized. For proton exchange, the extraordinary index increase Δne 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 Δne and a lower propagation loss. For proton exchange in lithium phosphate-diluted pyrophosphoric acid, a lower Δne 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 Δns 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 Δns, 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
Original Manuscript: July 28, 1995
Revised Manuscript: March 14, 1996
Published: September 20, 1996
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)