Sergey B. Odinokov

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.

A combination of computer-generated Fourier holograms and light guide substrates with diffractive optical elements for optical display and sighting system

A combination of computer-generated Fourier holograms (CGFH) and light guide substrate with diffractive optical elements (DOE) is described. The experimental results show that this combination can be used in display and sighting systems.

Optoelectronic array processor for identifying holograms with encoded latent images

This paper discusses methods of coding latent images in protective holograms in order to increase their degree of protection from counterfeiting and to automate the monitoring of their authenticity. It is proposed to use the operation of vector-matrix multiplication as a coding-decoding algorithm, carried out on optical signals by digital multiplication by means of analog convolution. Possible optical layouts for implementing the chosen algorithm are analyzed.

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.

Application of optoelectronic micro-displays for holographic binary data recorder based on computer generated fourier holograms

Present article highlights the researches provided during the development of holographic memory system based on application of computational methods to encode binary data pages as amplitude computer generated Fourier holograms (CGFH). Using electro-optical micro-display and projection optics CGFH can be recorded onto photosensitive medium. The type of display that is used in data recorder determines the specificities of optical scheme architecture with its own limitations and advantages. There are three projection schemes of binary data recorder discussed in the paper. A linear scheme based on transparency-type liquid crystal spatial light modulator (LC SLM), a scheme based on reflection-type liquid crystal on silicon spatial light modulator (LCoS SLM) which uses a beamsplitting cube, and the most compact and simple scheme based on self-emitting OLED-display. The results of experimental implementation of all the three projection schemes for CGFH of binary data pages record onto the holographic carrier and consequent optical reconstruction and analysis of the encoded data are presented.

Wave front sensor based on holographic optical elements

A wavefront sensor (WFS) based on holographic optical elements, namely computer generated Fourier holograms is proposed as a perspective alternative to the Shack-Hartmann sensor. A possibility of single and multimode sensor and the dependence of their characteristics were investigated.

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.

Research of a method and optical system for recording multiplex holograms in a system of holographic memory

The new modified holograms multiplexing method using normal to holographic recording media reference beam incidence and off-normal signal beams incidence is offered for application in holographic memory system having high information capacity and high data rate. Signal beams are located around reference beam concentrically. In this case quantity of multiplex holograms in the same area of recording media is equal to quantity of signal beams. Experimental holographic memory system model applying offered method is tested. Possibility of multichannel optical head application for data recording and retrieving is shown. Offered multiplexing method advantages consist in following: obviating of the necessity of recording media rotation; crosstalk noise free restored data page images; possibility of thin holographic recording media application.

Optical system of the device for making a hologram matrix

The optical system for writing down and reconstruction 2D hologram matrix, consisted of Fourier-holograms of data pages is developed. This system may be used in page-based holographic card storage devices, includes two separate parts--data writing and data reading devices. By this concept data writing down may be made by unique stationary device and data reading realized by some quite simple devices of different users. The hologram write down arrangement included laser source beam splitter, object, and reference parts. Object part includes beam telescope expander, 2D spatial light modulator, and Fourier-objective. Spatial light modulator forms input data page. Reference part include cylindrical lens beam expander, and 1D spatial light modulator. Reference beam is directed to the holographic media plane with the perpendicular incidence. The hologram matrix string is written down by simultaneously discrete moving of arrangement object part entries. Herewith the image placement of the input data page does not change. This hologram write down arrangement allows us to make data page reconstruction to the matrix photodetector directly by the light of compact semiconductor laser. Moreover, it is necessary to provide only 1D mechanical moving while data reading out from the hologram matrix.