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SiO 2 /TiO 2 /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 SiO 2 and TiO 2 concentrations. To produce low optical propagation loss in the waveguide, it was necessary to avoid the precipitation of TiO 2 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 TiO 2 was avoided in the TiO 2 concentration range of up to 30 wt %, resulting in low optical propagation losses in the slab waveguide configuration. In the higher TiO 2 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 TiO 2 concentrations, from 0% TiO 2 /50% SiO 2 /50% PVP to 50% TiO 2 /0% SiO 2 /50% PVP was achieved. The reactions of the sol-gel precursors were also studied using UV-visible and FT-IR spectroscopy.

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We report the generation and detection of a terahertz wave with a nonresonant electro-optical crystal using 1.56μm femtosecond laser pulses. Using a 0.5-mm-thick (110)-oriented GaAs wafer for optical rectification and electro-optical modulation, we detected spectral sensitivity below 3THz. We also estimated the availability of GaAs from the viewpoint of an electro-optical coefficient and phase match condition.

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