Vibrational overtone absorption of side chain in silicone at 1.55 mu m wavelength band

In order to estimate the propagation loss of a silicone resin optical waveg uide at 1.3 mu m and 1.55 mu m wavelength bands, the absorption spectra of silicone monomers with nondeuterated side chains are examined. A methyl gro up imposes an absorption loss around 1.55 mu m due to an absorption peak at 1.52 mu m, which is assigned to the combination overtone of C-H symmetric stretching at 2920 cm(-1) and methyl C-H rocking deformation at 800 cm(-1). We demonstrate that a cyclohexyl group, which has no fundamental vibration in the 600-850 cm(-1) range, exhibits a wider optical window at the 1.55 m u m band than the methyl group.