A highly sensitive excite and probe technique to measure optically induced refractive index changes in Ti:LiNbO3 -waveguide resonators

Abstract

Introduction. Severe limitations for the application of Ti:LiNbO3 optical (channel) waveguides especially in phase sensitive devices are set by the susceptibility of this material to optically induced changes of the (effective) indices of refraction (optical damage). Therefore several groups have thoroughly investigated this photorefractive susceptibility using different methods and waveguide devices such as asymmetric Mach- Zehnder interferometers, directional couplers and straight waveguides [1-3]. In planar waveguides using a holographic method optically induced changes of Δn ≃ 10−6 could be measured [4]. The understanding of the photorefractive effects in Ti:LiNbO3 waveguides has been considerally improved by the cited work. Nevertheless, an even more sensitive method is required to study these effects, as recent developments of waveguide fabrication techniques like codoping, ion exchange, outdiffusion and substrates of higher purity have reduced the damage susceptibility considerably. A method is needed which allows a quantitative assessment of the quality of — in particular channel — waveguides with respect to their photorefractive susceptibility.