Study on the photoreactive polymer materials based on epoxy matrix for holographic 3D data storage system

Abstract

Photoreactive polymers (i.e., photorefractive materials, photochromic polymers, and photopolymers) routes amplitude/phase gratings with volume or surface periodicity have been extensively studied in the past decade because of their potential applications as high-density data storage, holographic optical elements for waveguides, sensor/indicator for non-destructive diagnosis. However, recordable materials from photoreactive polymers are inherently unstable, which is detrimental to be used in practical applications. Effort is therefore being made to fabricate more robust photopolymers, reviewed in chapter I, which have high grating stability without sacrificing the holographic performance. To this end, epoxy-resin based crosslinked photopolymer, sensitive to green/blue laser, was fabricated in order to suppress writing-induced volume shrinkage. Basic concept is to use two-chemistry reaction as polymerization (i.e., epoxy-resin based matrix is cured by ionic-condensation mechanism whereas photosensitive materials are remained before holography irradiation because they are only sensitive to radical moiety). Initial works in chapter II and III have included fabrication of epoxy-resin based photopolymer system and its optimization process in order to achieve high holographic performance. Crosslinked matrix system based on epoxy resin would be beneficial to control the film thickness because epoxy-resin precursors exist as a liquid state, so that it does not need any solvent for preparing photopolymer film. In addition the photopolymer based on epoxy resin system maintains a good dimensional stability during photopolymerization. In spite of these, a high chain crosslinking density of epoxy resin system still causes a limitation in holographic performance. High crosslinking density dictates the matrix rigidity and hinders the diffusion of monomers for photopolymerization, resulting in an insufficiency energetic sensitivity. In connection with these, we introduce diff...