Optimized holographic data storage: diffusion and randomization

The control of the exposure patterns, which maximizes the capacity of a holographic recording medium, is of critical importance in any holographic data storage system. In this paper, we develop a method to theoretically explore linear photopolymer storage media in which a polymerization driven monomer diffusion process takes place. Using this method we examine a technique, involving randomly shifting the exposure pattern between exposures, to increase material capacity. The randomization acts to reduce the effects of past exposures by reducing the monomer concentration spatial distribution which arises due to those exposures. Following a detailed description of a series of assumptions and approximations, we derive an analytic formula, which allows us to explore the results of applying the technique. It is shown that, in the particular situation discussed, randomization can provide a useful tool in reducing constraints on the relaxation times necessary between exposures.