Photosensitive ormosil system for integrated optics

A photosensitive organically modified silica (ormosil) material has been developed for integrated optics applications. In this material, prepared via a simple one-step sol-gel process, the silica backbone is substituted with methacrylate groups to confer photosensitivity, and with phenyl and/or methyl groups to adjust the refractive index from 1.47 to 1.52. Ormosil films are spin-coated onto silica-on-silicon substrates, and waveguides are defined in the films using a 325 nm HeCd laser direct write system. The unexposed regions are then dissolved with isopropanol to leave the desired pattern of ridge waveguides, before baking. The width of the waveguides increases with the UV dose and the concentrations of the methacrylate groups and the photo-initiator. Waveguides with widths ≥5 μm have been written with UV doses of around 0.4 J/cm², and baked at up to 200°C without cracking. In the 1310 and 1550 nm communications windows, the major sources of optical loss are vibration overtones of OH and CH groups. The intensities of these absorption bands have been measured with infrared spectroscopy and photothermal deflection spectroscopy, and the effects of some strategies to reduce the concentration of CH and/or OH groups, including fluorination and higher baking temperatures, are assessed.