Holographic Digital Data Storage System Research Articles

Design of the Tracking Controller for Holographic Digital Data Storage

In this paper, we present a new tracking control method for holographic digital data storage systems. Holographic data storage systems that use disk media need a different tracking method from those that use optical and hard disk drives. Here, we present the design and implementation of the controller. Due to the intermittent characteristics of the tracking error signal (TES), the tracking controller is designed to regulate the tracking error only while valid TES is generated. Since the valid TES appears intermittently, we use a feedforward controller while the TES is not valid. Furthermore, the feedback control and the feedforward control are mode-switched depending on the RF sum signal level. We also show the stability of the closed-loop system employing the mode-switching controller. Experimental results show the effectiveness of the proposed tracking control algorithm. For a ±100 ?m repeatable run out at 1 Hz, we were able to reduce the TES to 3.13 ?m (1?) with mode-switching control.

Improved data search by zero-order (dc) peak filtering in a defocused volume holographic content-addressable memory

Defocusing the recording material away from the Fourier plane is necessary to reduce the strong dc component and produce a more homogeneous object beam distribution in the hologram plane in volume holographic digital data-storage systems with amplitude-modulated data pages. However, content-addressable searching with defocused recording results in higher cross-correlation peak intensities. We present a method for performing a faithful content-addressable search in a defocused volume holographic data-storage system. A new dc-filtered content-addressable search method for defocused volume holographic data-storage systems with binary data pages is demonstrated. Both simulation and experimental results are presented. The experimental results show good discrimination capability and confirm the feasibility of the proposed technique.

Improvement to holographic digital data-storage systems with random and pseudorandom phase masks

Various effects associated with using a random phase mask in holographic data storage are analyzed. It is shown that the nonlinear nature of recording a phase hologram coupled with the highly nonuniform profile of the object beam is the major source of interpixel cross talk. It is also shown that, although the nonlinear effects are reduced by an increase in the reference-to-object beam ratio, the scattering noise is increased. Thus an optimal beam ratio must be used to maximize the signal-to-noise ratio. It is demonstrated as well that the interpixel interference noise can be suppressed effectively by use of a multilevel pseudorandom phase mask, which also significantly reduces the nonlinear noise. These findings are supported by experimental results that show the signal-to-noise ratio and efficiency are improved significantly by use of a six-level pseudorandom phase mask.