Storage density limitation of a volume-type hologram memory: theory.

The maximum storage density of a volume-type hologram memory obtainable with a prescribed signal-to-noise ratio is discussed. In the theoretical analysis, a microscopic particle model of a phase hologram is considered; the refractive index variation is assumed to be caused by the density variation of bleached silver particles distributed spatially at random. The signal and noise intensities are derived from the analysis based upon this model. The theoretical limit of the storage density and the optimum hologram thickness are then derived in terms of the signal-to-noise ratio. The maximum storage density is finally given as a function of the average scattering cross section of the particles, the light wavelength, and the prescribed signal-to-noise ratio. Some practical cases are also discussed on the basis of measured material parameters.