Diffraction of Guided Optical Waves by Surface Acoustic Waves in Proton-Exchanged 128� Rotated Y-Cut LiNbO3

Abstract

The acousto-optic diffraction of guided optical modes by surface acoustic waves in the RamanNath regime in the single-mode optical waveguide formed by the proton exchange technique in 128 o rotated Y-cut lithium niobate has been studied. The experiments have been performed at the optical wavelength 0.6328 mm in a single-TM mode waveguide formed by treatment in pure benzoic acid for 20 min at 230 C and at the SAW frequency of 78 MHz. The measured dependences of the light intensity diffracted into the zeroth, first and second orders on the driving voltage are in good agreement with the theoretical calculations. The values for the acousto-optic figure of merit M 2 ¼ 9:5 Â 10 À15 s 3 /kg and the effective photoelastic cefficient p eff = 0.14 have been evaluated showing the efficiency of the acousto-optic interaction in proton-exchanged lithium niobate being comparable to that in the pure crystal.