Highly Efficient Organic/Inorganic Hybrid Nonlinear Optic Materials via Sol−Gel Process: Synthesis, Optical Properties, and Photobleaching for Channel Waveguides

The thermally stable second-order nonlinear optic (NLO) hybrid materials were successfully prepared by a sol−gel process using dye-attached sol−gel monomers (ormosils) of difunctionalized or trifunctionalized second-order NLO chromophores attached to silicon atoms. The dye-attached sol−gel monomers were synthesized by the coupling reaction of 3-isocyanatopropyltriethoxysilane with the corresponding functionalized NLO chromophores in DMAc. The dye-attached sol−gel monomers were homopolymerized and copolymerized with TEOS by hydrolysis and polycondensation in the presence of a slight excess amount of acidified water (pH 3), yielding the hybrid precusors (or a homogeneous solution). The hybrid precursors were spin-coated on various substrates such as ITO glass and NaCl disk. Hybrid films were further polycondensed by curing at 170 °C for 3 h. The cured hybrid materials existed in monohydroxy (T2, Q3) and nonhydroxy (T3, Q4) states, indicating the formation of a highly cross-linked silicon−oxygen polymeric network. All of the cured organic/SiO2 hybrid films are transparent. The organic/SiO2 hybrid materials were quite stable at elevated temperatures above 250 °C. The hybrid films were poled by corona discharge technique or dc contact electrode. The values of electro-optic coefficient for the organic/SiO2 hybrid materials were in the range of 3.7 to 16 pm/V at the wavelength of 1.3 μm, depending on dye-attached sol−gel monomers and poling conditions. The SG-DANS (1:2:2) film shows excellent temporal stability. The r33 signal remained at 80% of its initial value after heating even at 150 °C for 3 h. Also, the second-order nonlinear optical coefficient d31 of 72 pm/V for the SG-DANS (1:2:0) hybrid film measured by the Maker fringe technique was obtained. The refractive index was decreased after photobleaching. Using the hybrid film, a single-mode channel waveguide was also fabricated by the photobleaching method. The mode pattern confirmed that a channel waveguide was single-mode, and the optical propagation loss was measured to be less than 1 dB/cm.