Optical propagation losses and coupling losses in Ti-diffused strip waveguides, fabricated in y-plate and z-plate LiNbO(3), have been examined at 1.15-,microm wavelength. Propagation losses for y-plate and z-plate waveguides are ~0.5 dB/cm. Coupling losses in the y-plate and z-plate waveguides for a single-mode fiber are 2.5 and 1 dB, respectively. This difference is due to the large surface diffusion anisotropy; it is expressed by near-field pattern overlap calculations.

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Vanadium dioxide (VO2) film which has nearly the same transition point as single crystal has been obtained by reactive evaporation of vanadium on glass and subsequent annealing in N2 gas. Relations between optical properties of V02 film and its preparation conditions are presented. We made optical direct bit recording on V02 film using a laser diode as the light source. The threshold recording energy and bit density are 2 mJ/cm 2 and 350 bits/mm, respectively. We also made tungsten doping to lower the V02 film transition temperature.

Optical insertion losses in embedded strip waveguides fabricated in LiNbO3 by Ti diffusion have been examined at a 0.633-μm wavelength, taking into account resultant near-field patterns. It is confirmed that the main factors influencing optical insertion losses are radiation loss by the deficient refractive-index change of a waveguide, scattering loss by insufficient diffused residual titanium oxide film on a waveguide, and coupling loss between a waveguide and a fiber. A diffusion condition for making a low-loss waveguide is presented, although suppression of lateral diffusion is necessary to achieve further insertion-loss reduction.

A method for compensation of the index increment yielded by Li out-diffusion during Ti diffusion for the LiNbO3 waveguide formation is presented. Mg diffusion decreases the extraordinary refractive index, and its diffusion rate is far faster than that of Ti diffusion. An appropriate Mg diffusion condition is determined for eliminating the Li out-diffusion influence. Excellent optical confinement in the Ti-diffused LiNbO3 Y-cut strip waveguide is demonstrated with Mg diffusion.