Page-oriented holographic data storage systems (HDSSs) generally use spatial light modulators (SLMs) to generate twodimensional (2D) digital patterns, so-called data pages. These data pages are stored via interference patterns of the object and reference beam in the holographic medium and are retrieved from the medium by exposing it to the reference beam. The reconstructed data pages are then detected by a matrix detector. One important challenge in designing an HDSS is to develop a suitable modulation, which takes into account the specific characteristics of the transfer channel and enables high data capacity, high data transfer rate and low symbol error rate (SER). In this paper, we present a new method for modulating data in an HDSS. The main idea is to adapt the general concept of 2D run-length limited modulation (RLL) to a numerically more efficient implementation usable for HDSS. We demonstrate that this 2D block coding method with a constant weight and a sparse code increases the amount of user data per data page, while the SER remains low compared with standard sparse modulation coding. This results in a higher data rate and higher data density.

No abstract

A reflective counter-propagating holographic setup for optical data storage is presented. The system makes efficient use of the laser light by using the reference beam to generate the signal beam. After passing through the holographic medium, the reference beam is sent onto a spatial light modulator that directs the modified reference beam back into the holographic medium, where it interferes with the original reference beam. Thus 100% of the available laser power can be used for the reference beam. Furthermore, a special random phase mask and a corresponding data page format are introduced. The phase mask has an improved alignment tolerance of AE0:5 pixels in contrast to a conventional binary phase mask that has a tolerance of only AE0:1 pixels. Moreover, the mask still improves the shift-selectivity and eliminates the strong intensity peak in the Fourier plane. We investigate the shift selectivity and compare experimental and simulated results that were obtained with a two-dimensional fast-Fourier-transform (2D-FFT) volume integral method.

Holographic data storage is considered to be one of the most promising technologies for high-capacity data storage. Several holographic concepts have been suggested and investigated in detail by many companies. The concepts differ in the method of superposing object and reference beams inside the holographic medium. At present, the most relevant concepts are the plane wave concept, the collinear concept, and a concept with counterpropagating beams. We compare all three concepts, with regard to their beam overlap, efficiency of material consumption, diffraction efficiency, and crosstalk characteristics. The investigation is performed by numerical simulations, which offer welldefined conditions in all setups and are independent of experimental uncertainties such as the nonlinear behavior of medium sensitivity and the effects of light scattering or reflection.

We suggest a new method for data detection based on direct data identification and compare this new method with three commonly used methods based on decimation using linear transformations. To compare these methods, the complete procedure from data page creation, sending data through an optical channel, and data detection is simulated numerically. This is performed by varying the noise level, sampling factor, and spatial filter. The proposed method requires a higher computational complexity, but for a broad range of realistic system parameters, it enables lower symbol error ratios.