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Stability problems of LiNbO3 waveguide components for interferometric applications in the visible and near-infrared regions

Optical phase drifts of guided waves in LiNbO3 waveguides can be caused by two different physical effects: light-induced refractive index changes (photorefractive effect) and so-called DC drift effects. Both phenomena have been investigated experimentally by a special interferometric technique on simple channel waveguides with very high accuracy. Light- induced refractive index changes were measured at 633 nm wavelength and in the 800 nm region. These index changes in annealed proton exchanged (APE) waveguides are about one order of magnitude smaller compared to titanium indiffused (TI). This can be explained by an increased photoconductivity of the APE material. DC drift effects in APE waveguides, however, are quite large and cannot be reduced in the same way as for TI waveguides. This is due to an ionic charge transport process. MgO doping of the waveguide substrates leads to a considerable reduction of both the photorefractive effect and the DC drifts of APE waveguides. The influence of both drift effects on the stability of a three-beam interferometric displacement sensor was demonstrated.