Photopolymerization process and related devices

Abstract

A photopolymerization process is adapted for the production of various optical devices by means of a modified process which serves to increase the index change obtainable in a variable pattern of index of refraction. The process comprises the steps of flowing into place in a supporting structure a mixture of two components of differing reactivity and polarizability, partially polymerizing the mixture, writing a pattern of varying index of refraction in the partially polymerized mixture by further polymerizing it by suitable optical radiation in a corresponding pattern, and fixing the mixture against subsequent changes in polymerization. Typical components used in the process include a mixture of the monomers cyclohexyl methacrylate and N-vinylcarbazole together with benzoin methyl ether as a photosensitive initiator of polymerization, which proceeds by free radical reactions. In the limit of our technique, one of the components can have zero reactivity. This photopolymerization process is applicable to production of volume gratings in closed cavities having parts with constricted clearances therebetween, in which application it is impossible to evaporate unreacted components after the mixture has been flowed into place. The volume gratings are useful in distributed feedback lasers, in frequency sensitive optical filters and in channel-dropping arrangements for optical communication systems. Submerging the apparatus in which polymerization is to occur in an index-matching fluid between flat glass plates is an aid to producing uniform volume gratings in a cylindrical device.