ELSEVIER ADVANrEn zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Optics & Laser Technology, Vol. 28, No. 4, pp. 269-276, 1996 Copyright 0 1996 published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0030-3992/96 %15.00+0.00 0030-3992(95)00094-l .- .. ._-- TECHNOLOGY A review of aspects the improvement of memory technology relating to holographic N. N. VYUKHINA, I. S. GIBIN, V. A. DOMBROVSKY, S. A. DOMBROVSKY, B. N. PANKOV, E. F. PEN, A. N. POTAPOV, A. M. SINYUKOV, P. E. TVERDOKHLEB, V. V. SHELKOVNIKOV Results of studying a holographic memory to write/read digital data pages are presented. The research has been carried out in Novosibirsk, Russia. Great attention was paid to methods of improving recording density and the reliability of data reading, the development of ‘dry’ photopolymers that provide recording of superimposed three-dimensional phase holograms, and the designing of parallel optic input large-scale integration (LSI) for reading and logical processing of data arriving from the holographic memory. Copyright @ 1996 published by Elsevier Science Ltd. KEYWORDS: holographic memory Introduction Research in the field of holographic memory (HM) with a page data format has been carried out for more than 30 years. Important fragments of this history are presented in Ref. 1. Pappu2 has given a comprehensive critical review of this research. Besides the basic results obtained in the USA, Japan, and countries of Western Europe, a number of achievements in this area have been performed in Russia, specifically in Novosibirsk. We merely mention 32 x 32 liquid-crystal transparencies, a 128 x 128 laser beam Te02 deflector, a 32 x 32 integrated photomatrix, a randomization phase mask; all of which were carried out to create an operating model of the archival holographic memory on flat carriers3. A large array of microholograms, with real write/read digital data, and rich statistical information on the fluctuations of page images reconstructed from an array of microholograms and on the errors of data reading, were achieved4. Unfortunately, these efforts appeared to be deficient for the practical application of this kind of memory. This was caused by technological imperfections in the holographic memory elements, limitations of the silver halide emulsion being used as a recording medium, and an insufficient recording density (lo4 bit mm-2) and bit error rate (BER) of data (10-4-10-6). The impressive advances of semiconductor memory and optical disc memory also contribute to the reasons. The authors are in the Institute of Automation and Electrometry, Russian Academy of Sciences, Siberian Branch, Universitetsky pr. 1, 630090, Novosibirsk-90, Russia. Received 5 May 1994. Revised 4 April 1995. Over recent years, the opportunities of page-data holographic memory are again becoming attractive. This is specifically stimulated by the necessity for creating switched networks for mass-parallelism computers and neurocomputers. In these cases, optical images reconstructed from holographic memory are used to control the state of photoelectronic switches placed on chips in integrated circuits. Interesting opportunities for holographic memory applications also appear in designing database machines and knowledge- base machines. Therefore, proceeding from the requirements for modern large-capacity storage systems, on the one hand, and from holographic memory characteristics achieved earlier but which are not adequate, on the other, the authors undertook efforts to solve a few problems. (1) (2) (3) (4) To estimate a practically attainable limit of recording density on flat carriers. To estimate the efficiency of application in holographic memory of some commonly used systems for data coding as additional information means to reduce the level of reading errors. To find thick recording media with a ‘dry’ development process for recording superimposed three-dimensional microholograms; the superimposed recording in a thick medium was considered as a means to increase packing density. To design photoelectronic large-scale integration (LSI) that provides weak optical signals during photoelectric conversion of page images reconstructed from holographic memory and the further logical processing of the signals to solve associated search tasks. 269