Analysis of a collinear holographic storage system: introduction of pixel spread function

Abstract

Image formation in a collinear holographic storage system was analyzed. The wavefront from each pixel of a spatial light modulator was regarded as a plane wave in the recording medium, and its wave vector was determined by the position of the pixel. The hologram in the recording medium was treated as the summation of all gratings written by all combinations of two plane waves. The image of a data page was formed by diffraction of the reference waves by all gratings. The results of the simulation showed good agreement with experiment. We introduced the pixel spread function to describe the image formation characteristics. Analysis of the pixel spread function reveals that a radial-line pixel pattern for reference waves gave a sharper image than other reference pixel patterns. It is also shown that a random phase modulation applied to each reference pixel improved the image formation.

Diffraction Property of Collinear Holographic Storage System

“…( [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], it shows that the PSF is related to the auto-correlation function of the reference pattern times a defocusing phase term. Accordingly, a lens array used as the reference is introduced.…”

“…The first is to calculate the point spread function (PSF) through Bragg mismatch [10,11]; the second is to apply Fresnel transform to simulate the light field in the recording disc and through Born's approach or the method called "volume hologram being an integrator of the lights emitted from elementary light sources" (VOHIL) to calculate the diffraction pattern on the CCD plane [12][13][14][15]. The procedures of the approaches are described in detaisl from Refs.…”

“…(1-13) and Eq. (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). When the disk shifts, based on VOHIL model, the optical field diffracted from specific layer at a depth (Δz) can be expressed (1-31)…”

Implementation of single-beam multiplexing encoding with a dually modulated spatial light modulator

“…Besides this, the two paths should be well aligned and delicately adjusted for multiplexing encoding and decoding, which means the system is very large and complicated. Recently, Horimai et al [16], Shimura et al [17], and Horimai and Tan [18] proposed a collinear holography for disk data storage. By using a digital micromirror device (DMD) as spatial light modulation, they implemented a recording and reconstructing system in a single optical axis.…”

“…As an essential element in the system, the TN-LCD is modulated in two modes: amplitude-mostly modulation and phase-mostly modulation. Compared with collinear holography [16][17][18], our system is more flexible and will enhance the storage capacity to a higher level. Besides, this singlebeam encoding system should be a good choice for secure data encryption and decryption, as the signal is encoded in the multiplexing hologram with the reference beams of different encoded phase modulation.…”