Pre-enhancement for High Spatial Frequency in Holographic Memory

Abstract

In holographic memory, a signal beam spatially modulated by a data page passes through a lens and aperture on the Fourier transform plane. The data page is spatially sampled because the spatial light modulator and camera sensor have pixel structures. This means that the high-spatial-frequency components of the data page are eliminated or that their amplitude decreases; therefore, the brightness uniformity and signal quality of the reconstructed data page deteriorate. We developed a pre-enhancement technique for high spatial frequencies that can alleviate the deterioration and experimentally confirmed its effectiveness. Data pages including random data were recorded and retrieved using a pre-enhancement function defined from the measured spatial-frequency response of the optical system. The technique reduced the number of bit errors in the reproduced image by 80% or more in comparison with images reproduced without this technique.