Modulation coding for pixel-matched holographic data storage

Abstract

We describe a digital holographic storage system for the study of noise sources and the evaluation of modulation and error-correction codes. A precision zoom lens and Fourier transform optics provide pixel-to-pixel matching between any input spatial light modulator and output CCD array over magnifications from 0.8 to 3. Holograms are angle multiplexed in LiNbO(3):Fe by use of the 90 degrees geometry, and reconstructions are detected with a 60-frame/s CCD camera. Modulation codes developed on this platform permit image transmission down to signal levels of ~2000 photons per ON camera pixel, at raw bit-error rates (BER's) of better than 10(-5). Using an 8-12-pixel modulation code, we have stored and retrieved 1200 holograms (each with 45,600 user bits) without error, for a raw BER of <2x10(-8).

Two-dimensional binary halftoned optical intensity channels

“…Such 2D optical intensity channels have been used in a variety of applications such as holographic data storage [1][2][3], page-oriented optical recording [4,5], 2D barcodes [6,7], and multiple-input/multiple-output (MIMO) wireless optical communications [8][9][10][11]. A major practical problem of many of these applications is the requirement of strict alignment between the transmitter and the receiver in order to avoid inter-channel interference [1,2,12].…”

“…A major practical problem of many of these applications is the requirement of strict alignment between the transmitter and the receiver in order to avoid inter-channel interference [1,2,12]. Such a system is termed "pixel matched", i.e.…”

Modulation Codes for Optical Data Storage

“…With a constant-weight page, low-complexity correlation detection can be efficiently implemented (Coufal et al, 2000;Burr & Marcus, 1999;Burr et al, 1997). Two kinds of weight distribution garner interests of researchers.…”

“…The 6:8 balanced block code (Burr et al, 1997) is one of the most common block modulation codes used in the holographic data storage systems. A group of six information bits is encoded into a 2×4 block with exactly four ON pixels and four OFF pixels, satisfying the balanced constraint.…”

“…Since 70 8 4  C is larger than 2 6 =64, we choose 64 patterns from 70 code blocks and assign Gray code to these blocks . Correlation detection (Burr et al, 1997) is also proposed to decode such block code. In this method the correlations between the retrieved block and all code blocks are computed and the code block with the maximum correlation to the received block is declared the stored pattern.…”