Sol-gel fabrication and properties of optical channel waveguides and gratings made from composites of titania and organically modified silane

Optical waveguide thin films have been prepared from composites of TiO₂ and organically modified silane (ormosil) at low temperature by the sol-gel technique, using γ-glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as precursors. Atomic force microscopy and ellipsometry have been used to characterize the morphologies and properties of the waveguide thin films deposited on compound-semiconductor and silicon substrates. These results indicated that a dense and porosity-free waveguide film could be obtained at 100°C. The refractive index of the film could be varied from 1.44 to 1.55 at 633 nm by varying the titanium content. It was experimentally demonstrated that a channel waveguide and grating structures could easily be fabricated for these composite thin films by etching and embossing. It was found that this method is specifically useful for the fabrication of diffractive grating and optical planar waveguides on sol-gel-derived glass films coated on temperature-sensitive substrates such as III-V compound semiconductors. By this means, channel waveguides have been fabricated using laser writing and reactive ion etching or wet etching, and gratings with a period of 1.102 μm and depth of 57.2 nm have also been obtained by embossing.