Cyclic allylic sulfide based photopolymer for holographic recording showing high refractive index modulation

The development and characterization of a new holographic photopolymer system showing high refractive index modulation (∆n) is presented. It exploits the ring-opening polymerization reaction of a cyclic allylic sulfide (CAS) monomer, which is dispersed in a cellulose acetate butyrate (CAB) polymer matrix together with a blue sensitive radical photoinitiator. Volume Phase Holographic Gratings (VPHGs) obtained using these films show a very good fidelity of the transferred pattern, without deviations from the theoretical curves. A high ∆n is obtained due to the addition to this system of a tetrafunctional thiol crosslinker, which maximizes the material potential (formula limit) of the formulation. It also allows for a thermal post process of the gratings, further enhancing the ∆n. The photopolymer properties are evaluated as function of the monomer and thiol concentration to determine the optimal composition, at which a ∆n greater than 0.03 is obtained. This is a considerably high value in the field of photopolymers for holography and it enables the manufacturing of efficient holograms.