In this study, two classes of low-loss optical planar waveguides were prepared from trialkoxysilane-capped poly(methyl methacrylate) (PMMA)-silica and PMMA-titania hybrid materials, respectively. The prepared hybrid films had very uniform structure and surface planarity. The incorporation of the silica or titania segments into the acrylic polymer matrix reduced the intermolecular interaction and thus induced an increase in anharmonicity of the C-H bond in the acrylic segment. Therefore, the third harmonic stretching vibration absorption of the C-H bond was red-shifted and resulted in a tuning of near-infrared (NIR) optical absorption. The optical loss of the studied waveguides was reduced from 0.65 dB/cm of the PMMA waveguide to 0.26 and 0.28 dB/cm with increasing the silica and titania content in the hybrid materials, respectively. The reduction of the C-H number density and shifting of the NIR absorption spectra accounted for the relationship between the optical loss and the inorganic oxide content. The increased anharmonicity through the incorporation of the inorganic moiety in the hybrid materials provides another approach for tuning the NIR optical properties. (c) 2005 Wiley Periodicals, Inc.