ZnO-diffused lithium niobate waveguide polarization controller

Abstract

The linear electro-optic effect in lithium niobate is capable of realizing a variety of polarization transformations, including TE-to-TM and left-to-right circular polarization conversion. While most LiNbO3 components are designed for operation in the third telecommunications window around 1.55 μm wavelength, current interest in quantum information processing and atomic physics, where the wavelengths of interest are in the visible and near-infrared, has placed new demands on endless polarization control devices. At short wavelengths, traditional Ti-diffused LiNbO3 waveguides suffer from photorefractive degradation at optical power levels well below 1 mW. Proton exchanged waveguides have much higher power handling capability but can only guide light polarized parallel to the optic axis, and therefore are not applicable to polarization control. Zinc oxide diffusion is an alternative waveguide fabrication technology that guides both e- and o-waves with much higher power handling capability than Ti:LiNbO3 waveguides. ZnO:LiNbO3 waveguides exhibit a highly circular mode field with lower anisotropy than Ti-diffused waveguides. We report on the modeling, fabrication and testing of a polarization controller in ZnO-doped, x-cut lithium niobate operating at a wavelength of 780 nm.