Second-order optical nonlinearities in dilute melt proton exchange waveguides in z-cut LiNbO3

Abstract

Planar optical waveguides with different refractive indices are made in z-cut LiNbO3 with a dilute proton exchange method using a system of glycerol containing KHSO4 and lithium benzoate. The optical second-order susceptibilities of these waveguides are measured by detecting the 266 nm reflected second-harmonic signal generated by a 532 nm beam directed onto the waveguide surface. It is found for this kind of waveguides that in the waveguide region all the second-order susceptibilities take values of at least 90% of the original LiNbO3 values for refractive index changes less than ∼0.013 at the 632.8 nm wavelength, whereas the susceptibilities are strongly reduced for larger index changes.