Generation of graded index profile by photochemistry

Abstract

It is well known the cinnamoyl group reacts to 350nm wavelength UV light and forms crosslinking bond by photodimerization. Such change in the structure would cause the change in the refractive index. When fiber is exposed to the UV light, penetration of light will be decreased according to the depth. Therefore graded index polymer optical fiber (GI-POF) with photopolymers can be made by photochemistry. For this study, monomer was synthesized whose main structure is similar to Methyl metacrylate and which has cinnamoyl functional group as a side group. And copolymerization with Methyl metacrylate is performed because cinnamate homopolymer has poor physical properties and high cost and MMA is good polymer for optical transmission. From the refractive index change mechanism of the cinnmoyl group, it could be anticipated that there is kind of relationship between IR peak intensity ratio of C=C double bond and refractive index. The result shows linear relationship between them. Therefore it was possible to obtain the refractive index profile using IR peak intensity ratio. The change of refractive index was surveyed as various contents of cinnamoyl group and refractive index profile as irradiation time. The results show enough change of refractive index when content of cinnamoyl group is over 10 mol% and proper profile shape could be obtained by the change of irradiation time.