A photolocking method is used in polymer materials in which the refractive index and thickness of a thin polymer film is selectively increased by photochemical reaction. Samples are initially prepared in the form of thin polymer films containing a moderately volatile dopant. Photochemical reactions are used to reduce the mobility of the dopant and thus fix it in the film. The dopant in the unexposed regions is then removed by heating. If the refractive index of the dopant is higher than that of the polymer, the sample will then have higher than that of the polymer, the sample will then have a higher index in the exposed areas than in the unexposed areas. There is also a modulation of the thickness of developed film. These methods have approached the fabrication of integrated optical circuits. Fabrication of components for integrated optics by photolithography or laser beam writing without any additional production step such as development is very attractive.
The solution sol-gel method is used to produce thin films of photosensitive hybrid organic-inorganic glass on silicon. Glasses consist of photoinitiator, methacryloxyprolpyltrimethoxysilane (MPTMS), methacrylic acid, and zirconium propoxide (ZPO) are suitable for fabricating optical components such as ridge waveguides and Bragg diffraction gratings by solvent assisted development. The photosensitive dopants are 2,2-Dimethoxy-2-phenylacetophenone (Benzildimethylketal : BDK), Benzophenone (BP), and 2-Hydroxy-2-methylpropiophenone (DAROCUR 1173). These films showed both refractive index and thickness change after selective UV irradiation and drying. Thus the patterned films can be used fabricating devices without development process.
The thickness, refractive index, and refractive index profiles of various photoinitiator doped sol-gel hybrid glass films were measured by using prism coupler. The films were irradiated by UV dose increasing from 0J/$cm^2$ to 243J/cm^2$ and dried in oven. After UV irradiation through mask and drying of films, photopatterned film was obtained and confirmed by optical microscopy.
The molecular structures were investigated by FT-IR spectroscopy and UV-spectrophotometer with UV dose before and after drying. After drying, in the unexposed films, the phenyl group peak of photoinitiator was disappeared but in the irradiated films these peaks were remained. After UV exposure, the new peak is formed by attachment of benzoyl radical to the matrix in the case of BDK and D1173.
The fixing of photoinitiator in the matrix after UV irradiation was confirmed by differential scanning calorimetry (DSC). After UV irradiation, the endothermic peak of dopant was disappeared.
The optical absorption at 1550nm was increased after adding benzildimethylketal (BDK). Benzildimethylketal(BDK) caused significant increase in the waveguiding loss at high doping concentration.
