Quantitative investigation of photorefractive effects in LiNbO3 channel waveguides

Abstract

A novel interferometric technique for measurements of optical phase changes in channel waveguides is described. It is based on a simultaneous excitation of two neighbouring channel waveguides with adjustable intensity ratio. Phase changes are deduced from the shift of an interference pattern formed by the superposition of the two collimated output beams. This technique has been applied to measurements of lightinduced refractive index changes (photorefractive effect) in LiNbO3 optical channel waveguides. Systematic investigations on LiNbO3:Ti waveguides show that both the magnitude and the time constant of lightinduced index changes depend characteristically on guided wave power. Light-induced waveguide losses become significant only, when the guided-wave power leads to waveguide cut off. The light-induced processes of index changes can be reduced considerably after the Ti-indiffusion by simple thermal treatments. In channel waveguides, produced by proton exchange (PE) followed by an annealing process, light-induced index changes are smaller, but develope faster than in Ti indiffused waveguides, thus indicating an increased photoconductivity inside the proton exchanged material. At A=B3O nm photorefractive effects are reduced by about one order of magnitude compared to ?=633 nm.