Light deflector using a chalcogenide amorphous loaded LiNbO_3 waveguide

A large-angle Bragg deflector has been demonstrated, utilizing the photoinduced refractive-index change in an As-Se-S-Ge amorphous film loaded on a Ti-diffused LiNbO3 waveguide. Modal analysis shows that optical fields and effective indices in a LiNbO3 wavelength are affected strongly through the index change in the amorphous overlayer. Coupling coefficient and interaction length of the deflector are derived analytically by the coupled wave theory. Interaction length becomes short rapidly with increasing the refractive-index change of the grating or the loaded film thickness. An almost 40° deflection has been achieved experimentally with a 0.7-μm grating pitch and 1-mm interaction length.