Electric-field-switchable stratified volume holograms in photorefractive polymers

Two- and four-layer stratified volume holograms have been fabricated from the photorefractive polymeric material poly(methyl methacrylate): (1,3-dimethyl-2,2-tetramethylene-5-nitrobenzimidazoline):C(60) and characterized by holographic four-wave mixing experiments. Coherent addition of diffracted fields from the individual layers is observed, leading to a diffraction efficiency that increases with the square of the active layer thickness. Electricfield switching of the diffraction efficiencies of individual layers is demonstrated. The angular selectivity of the diffraction efficiency is also characterized for one, two, and four active layers. The angular width of the peaks narrows with increasing total structure thickness in agreement with theory.