A promising way of fabricating integrated optics components is based on the sol-gel synthesis and photocuring of organic-inorganic hybrid materials. However, the main factor limiting the development of passive devices is the propagation losses. Moreover, the possibility to compensate these attenuations by optical amplification is competed with the multiphonon relaxation associated to the presence of OH groups. To our knowledge, OH groups were always shown as the main responsible for attenuation at the telecommunication wavelengths, namely at 1310 and 1550 nm, although the matrix is composed of organic species which can contribute to absorptions in this spectral range. This paper deals with spectroscopic and optical characterizations of a well established organic and inorganic hybrid material in order to determine the contribution of each molecular groups to the attenuation at the aforementioned wavelengths.