Maximum effective optical thickness of the gratings recorded in photopolymers

Abstract

In recent years the development of new holographic memories based in photopolymers have a great goal. A new commercial holographic memories has been optimized by Aprilis and Inphase. The advantages of this type of materials to store information are well know: their high capacity and their fast random access. In the behaviour of this type of material two important factors determinate the quality of the material, the capacity and the energetic sensitivity. The base of the high capacity of the holographic memories is the high Bragg’s angular selectivity. The narrow curve of the angular scan are obtained when the effective optical thickness of material is high and permits record many holograms turning the plate only 3°. Others important factors are the dye and monomer concentration, high values of the concentrations origins high values of the index modulation (higher stored capacity, better energetic sensitivity and large dynamic range) but in when the dye and monomer concentrations are high all the light is absorbed in the first 200 μm of the material and the effective optical thickness of the grating recorded decrease (decrease the stored capacity) and the values of the noise are high in this case. In this work this attenuation of the index modulation in depth is having into account using rigorous couple wave theory to obtain the limit of the effective optical thickness for each composition of photopolymer. The optimal composition to obtain high stored capacity, high index modulation, good energetic sensitivity, high dynamic range and low noise are found.