Optical properties of an ormosil system comprising methyl- and phenyl-substituted silica

We report an organically modified silica (ormosil) system in which the refractive index can be varied from 1.40 to 1.55 by modifying the silica backbone with phenyl and methyl groups, which increase and decrease the refractive index, respectively. By changing the quantities of the phenyl- and methyl-modified precursors in the sol-gel mixture, the refractive index can be varied while keeping the organic fraction of the material constant. Crack-free, dried films up to 15-μm thick have been coated onto silicon and glass substrates, with potential application to optical waveguides for planar integrated circuits. The contributions of SiO-H and C-H absorptions to the attenuation in the communications windows are discussed, along with factors affecting the homogeneity and cracking tendency of the ormosils.