Improved Signal-to-Noise Ratio Using Phase Compensation in Shift- and Angle-Multiplexed Holographic Data Storage

Abstract

The phase compensation method and the use of a speckled reference beam was proposed for use in a shift- and angle-multiplexed holographic data storage system. As phase is random in a speckled reference beam, we multiplexed a plane wave with a speckled reference beam. Using this method enabled us to suppress phase fluctuations, and we thus increased the signal-to-noise ratio (SNR) by 2.2 dB in digital data. The theoretical limit of bandwidth and resolution of phase was also considered. The bandwidth of the phase modulator was made the limit of the control bandwidth in the current system. Widening it enabled us to create a more stable holographic data storage system with a higher SNR.

Two high-density recording methods with run-length limited turbo code for holographic data storage system

“…In fact, the distribution actually has a near-Nakagami-Rice distribution. 30) The second reason also concerns the LLR calculation. To calculate the LLR from Eq.…”

High-speed reference-beam-angle control technique for holographic memory drive

“…In other words, if the control input of the second FSC is designed as relative values such as in Eqs. ( 26) and (27), AFSC is able to control the reference beam angle to the Target Angle by using the angleerror-signal and the maximum diffracted beam intensity is achieved.…”

“…[15][16][17] The optimum reference beam angle during reproduction varies owing to distortion of the medium. The distortion is caused by, for example, temperature variation, beam irradiation, and moisture absorption, [18][19][20][21][22][23][24][25][26][27] and induces deterioration in the quality of reproduction. Thus, a reference-beam-angle control technique to position the reference beam at the optimum angle is crucial.…”

Control of Angular Intervals for Angle-Multiplexed Holographic Memory

“…Many multiplexing methods for holographic memory have been proposed, including coaxial-type multiplexing, 3) phase-coded multiplexing, 4) random shift multiplexing, 5) and angle multiplexing. 6) The angle multiplexing method can increase the storage density when it is used together with phase conjugation reproduction 7) and polytopic multiplexing.…”