Light-induced densification and mechanisms in hybrid sol-gel glasses for photonic devices

We give an account of the use of in situ waveguide Raman spectroscopy to provide vibrational information about structural changes that occur when a hybrid organically modified silicate glass is irradiated with UV or visible photons. The method is useful for 'reading' what transpires in an optical waveguide device as it is being formed by photoinscription methods. We describe a novel method for photoinscribing a circular (d equals 10 micrometer) optical fiber core on a SiO2-coated Si wafer. This is achieved by photolysis of a visible light photoinitiator in a slab waveguide while a standing wave is established in the film with the 514.5 nm TE0 mode of an argon ion laser. Simultaneous waveguide Raman spectroscopy (WRS) gave insight into structural changes in the matrix that ensue when the matrix is irradiated. As with UV induced densification, polymerization of the methacrylate groups by photoinitiation with visible light triggers further polycondensation reactions between unconverted equalsVSi-OCH3 and equalsVSi-OH to tighten the glass matrix.