Holographic data storage using phase-only data pages

Abstract

The application of phase-only input data pages has several advantages with respect to conventional amplitude modulated holographic storage: It avoids the saturation of the storage material by providing a smooth Fourier plane, improves the response in associative read-out, increases the light efficiency of the recording object wave and provides the opportunity of data encryption. However, if the information is carried by the phase of object wave front recovery of the data from the reconstructed beam is problematic with simple intensity sensitive devices as a CCD camera. To solve this problem we propose a compact phase to amplitude data page conversion method and apply it to the output of a Fourier holographic data storage system. The phase to amplitude conversion uses a birefringent crystal to generate two equal intensity copies of the reconstructed data page that are geometrically shifted by an integer number of pixels with respect to each other each other. The interference of these two phase modulated images is projected on the detector field of the camera. The interference pattern contains low and high intensity pixels if the phases of the interfering pixels are opposite and identical respectively. Using proper data coding, the original data matrix recovered from the intensity pattern of the CCD. Fourier plane homogeneity, bit error rate and positioning tolerances of the proposed holographic storage method are investigated by computer modeling and a comparison is provided with amplitude modulated data pages.