Sol-gel-proceseed SiO2/TiO2/poly (vinylpyrrolidone) composite materials for optical waveguides

SiO2/TiO2/poly(vinylpyrrolidone) (PVP) composite materials processed by the sol-gel technique were studied for optical waveguide applications. Change of refractive index through the range 1.39-1.65 at 633 nm (optical wavelength) was achieved by varying the ratio between the SiO2 and TiO2 concentrations. To produce low optical propagation loss in the waveguide, it was necessary to avoid the precipitation of TiO2 particles caused by the fast hydrolysis reaction of titanium alkoxide. By using titanium ethylhexoxide as a titanium alkoxide together with acetic acid and 2-propanol as the solvent, the precipitation of TiO2 was avoided in the TiO2 concentration range of up to 30 wt %, resulting in low optical propagation losses in the slab waveguide configuration. In the higher TiO2 concentration range, an additional measure, peptization was necessary. With this method, we could produce optical waveguides possessing optical propagation losses of 0.62 dB/cm or lower at 633 nm. Low optical propagation loss in all the TiO2 concentrations, from 0% TiO2/50% SiO2/50% PVP to 50% TiO2/0% SiO2/50% PVP was achieved. The reactions of the sol-gel precursors were also studied using UV-visible and FT-IR spectroscopy.