Optical near-field measurements of guided modes in various processed LiNbO3 and LiTaO3 channel waveguides

Abstract Scanning near-field optical microscopy (SNOM) technique has been used in collection mode to probe the evanescent field at the surface of channel waveguides fabricated in LiNbO 3 and LiTaO 3 either by ion exchange, titanium in-diffusion or ion implantation. A specific sample holder has been developed on a commercial system. The intensity distribution of guided modes in the different waveguides, and the associated topographical images, have been obtained and compared among them, giving relevant information about the structure of the various waveguides. The effective index of guided modes has been deduced from the measurement of the intensity variation of the evanescent field as a function of the distance from the waveguide surface.