V. I. Bobrinev

Holographic memory optical system based on computer-generated Fourier holograms

Holography is known to be a prospective tool for storing large amounts of digital information, providing long lasting safety and high speed data access. In this paper, we present a new approach to holographic memory system design. Our method is based on an application of discrete Fourier-transform calculations to encode two-dimensional binary data pages as computer-generated amplitude Fourier holograms (CGFHs). These CGFHs, represented as grayscale raster images, can be displayed with the use of a high resolution amplitude spatial light modulator (SLM) in an optical projection system and exposed on holographic medium with multiple reduction. The optical scheme required for the technical realization of this method appears significantly simpler compared with known holographic memory recording devices; moreover, it can be built using either coherent or incoherent light sources. Coding of data pages by precise pseudorandom phase masks during CGFH synthesis allows us to achieve about 3% of the recorded microholograms diffraction efficiency. The experimental results of CGFH projection recorded with a 20× reduction on photosensitive holographic medium and its reconstruction are presented.

Holographic memory system based on projection recording of computer-generated 1D Fourier holograms.

Utilization of computer generation of holographic structures significantly simplifies the optical scheme that is used to record the microholograms in a holographic memory record system. Also digital holographic synthesis allows to account the nonlinear errors of the record system to improve the microholograms quality. The multiplexed record of holograms is a widespread technique to increase the data record density. In this article we represent the holographic memory system based on digital synthesis of amplitude one-dimensional (1D) Fourier transform holograms and the multiplexed record of these holograms onto the holographic carrier using optical projection scheme. 1D Fourier transform holograms are very sensitive to orientation of the anamorphic optical element (cylindrical lens) that is required for encoded data object reconstruction. The multiplex record of several holograms with different orientation in an optical projection scheme allowed reconstruction of the data object from each hologram by rotating the cylindrical lens on the corresponding angle. Also, we discuss two optical schemes for the recorded holograms readout: a full-page readout system and line-by-line readout system. We consider the benefits of both systems and present the results of experimental modeling of 1D Fourier holograms nonmultiplex and multiplex record and reconstruction.

Investigation of Computer-Generated Fresnel Holograms for Wavefront Sensors

The possibility of using computer-generated Fresnel holograms to determine phase aberrations of a wavefront is studied. The results of computer simulation of the propagation of an elementary signal based on the Fresnel integral transform are presented. The principle of operation of a hologram for a wavefront sensor is discussed.

Specificities of data page representation in projection type optical holographic memory system

The matter of the present article covers the results obtained during the development of holographic memory record system based on projection of computer-generated amplitude Fourier holograms. The basic issue is the investigation of representation specificities of binary data pages, which were choose to be encoded on computer-generated amplitude Fourier hologram and then recorded on photosensitive medium as microhologram using simple projection optics and spatial light modulator. Limitations of data page resolution caused by limited resolution of SLM that is used to display the digitally synthesized holograms are discussed. Also the results of random phase coding of data page during the holograms synthesis research are presented.

Recording holographic memory device based on computer synthesis of Fourier holograms

Holographic memory systems provide such advantages as long data storage term, high data density and do not need a power supply. But traditional holographic systems require vibration isolation and are rather complicated. So computer generation of Fourier holograms (CGFH) is proposed. Instead of recording interference pattern, it is calculated on computer. High information density is reached in new method by multiplexing 1D Fourier Holograms. Optical equivalent of the 1D Fourier holograms computer synthesis is listed. Different spatial light modulators are analyzed for displaying CGFH. System for hologram recording is described. Results of recovering information CGFH are also listed.

Read-out optical schemes for holographic memory system based on multiplexed computer generated 1D Fourier holograms

Computer holographic synthesis allows to significantly simplify the recording scheme of microholograms in holographic memory system as the classic high precision holographic setup based on two-beam interference is removed by simple scale reduction projection scheme. Application of computer generated 1D-Fourier holograms provides the possibility of selective reconstruction of the multiplexed holograms with different orientation of data lines by corresponding rotation of anamorphic objective (cylindrical lens), used in the read-out systems. Two configurations of read-out optical scheme were investigated by our team: full-page scheme and line-by-line scheme. In the present article we report the specificities of these schemes and consider their advantages and disadvantages. The results of experimental modeling of both read-out configurations are also presented.

Holographic memory based on computer generated Fourier-holograms

Classic holographic memory systems use two-beam approach based on fixation of interference pattern between object and reference coherent beams on holographic recording medium. The size of single pattern is about several micrometers. High precision optical set up is required to form such a microhologram, that is the reason of excessive price for holographic recording devices. Methods of computer holographic synthesis allow to calculate holographic patterns numerically as 2D images. These images can be realized with the use of spatial light modulator, then reduced in optical projection system and exposed on holographic medium. In this paper we represent the research of holographic memory system based on computer generated Fourier holograms projection.