Abstract

Low-loss optical waveguides made of mixed thin films of SiO₂–Ta₂O₅ have successfully been fabricated by the rf magnetron sputtering method on thermally oxidized silicon substrate. The film exhibits wide controllability of refractive index by changing the composition ratio of SiO₂ and Ta₂O₅, which is attained by controlling the input rf power into each SiO₂ and Ta₂O₅ target during cosputtering. Thermal annealing is applied to the films after deposition. This process gives a remarkable decrease in propagation loss. Experimental results show that the refractive index is controlled in the wide range between 1.46 and 2.12 measured at 0.633-μm wavelength. This is linearly proportional to the mixture ratio of the two target materials. Propagation losses as low as 0.2–0.3 dB/cm at wavelengths of 0.633, 1.30, and 1.55 μm, are obtained by annealing the films at 400°C. Three-dimensional waveguides have been fabricated by a RIBE technique. Well-confined single-mode wave propagation is observed for the waveguide consisting of a rectangular core SiO₂–Ta₂O₅ guide surrounded by an SiO₂ cladding layer. The use of 3-D waveguides in a directional coupler is discussed.

© 1988 Optical Society of America