Directional couplers fabricated via a sol–gel route and conventional optical lithography

This work presents directional couplers fabricated by wet chemical etching of sol–gel derived inorganic silica–titania (SiO₂:TiO₂) waveguide films. In the work there are presented the results of theoretical analysis, applied technological procedure and results of experimental study of the directional couplers. In theoretical analysis we applied the Field Mode Matching method. In all technological processes involving masking, conventional optical lithography were used. A photoresist was used as a mask in the chemical etching processes. The water solution of ammonia fluoride was used as an etchant. Rib waveguides of 6 nm rib height and of rib width equal 2 μm were monomode for a wavelength of λ = 677 nm. The attenuation determined for fabricated rib waveguides is approximately equal to 1.7 dB/cm. The results of theoretical analysis are in excellent agreement with experimental ones.