We propose the approach to designing a holographic disk memory with high storage density and high recording-reading rates. The approach consists in the synthesis of 3-D memory by overlapping 1-D expanded partial holograms on a moving cather (disk) and the use of collinear optical heterodyning for data readout. The general architecture of such a memory is presented. The experimental results on recording and reading of wideband if signals in the acoustooptical scheme are demonsirated.L INTRODUCTEON Informalion storage devkes th high capacity and high recording-reading rates are necessary for up-to-date computer systems, mulliniedia, for environmental mothtoring, conservalion of the TV programs (in particular High-defmilion TV programs) and other data handling systems. The advanced way of this problem solution is the implementalion of the holographic approach.This approach consists in the synthesis of 3D holographic memory by overlapping 1-D expanded partial holograms of informalion pieces on the moving carrier (disk). If the informalion to be recorded is received in the form of AM, FM, analog or digital if wideband signals, the acoustooplical (AO) devices are most suitable for design of holographic memory systems, and especially with the lime integrating technique1.But usual AO scheme with only temporal modidation of signal point source and angular scanning by only the reference beam gives some problems. The ifbandwidth-duraiion product for the reference AO deflector must be four limes greater than that for piece of rf signal to be recorded. The regeneration lime of the reference beam must be less than duralion of one element of signal to avoid the losses in recorded information. This means the reference AO deflector having two channels which wodc in turn with very short lime of elecironic and optical switching.In this work, the new approaches and AO schemes for eliminating these problems and some results of experimental invesligations are described. , THE PRINCIPLE OF HOLOGRAM RECORDING AND READING DEVICETo eliminate the problems mentioned above the principle of double counter scaming (DCS) in AO device for recording the rf signal by lime integrating was developed. This principle assumes simultaneous and counter scanning by both the reference source and the focused spot ifiuminaling the signal AOM. 120 SPIE Vol. 2969 • 0-8194-2375-01961$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/26/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
The change ofthe dark relaxation rate of the bacteriorhodopsin (BR) hologram diffraction efficiency with write pulse width is considered. The heating of the BR film with light pulses is shown to be the cause. The effect ofthermal exposure can be reduced by increasing the hologram spatial frequency. . INTRODUCTIONBR-based dynamic photocamers are widely used for holographic data recording in information processing and storage st"2 The performance of such systems is affected essentially by the rate of recording and regenerating the data on the carrier. To acheive fast operation rate, the recording in the metastable state M of BR should be applied. 3 We found, that the thermal energy emitted during the recording in metastable state M can markedly exceed the optical energy losses of recording light pulse. And rapid heating of carrier in recording can initiate the thermal hologram generation.In this paper, the mechanism of carrier heating in recording is discussed. The attention is paid to the features ofthennal hologram which is caused by the thermal change in refractive index ofthe carrier under it's rapid heating. THERMAL EFFECTS IN FAST RECORDiNGFor fast recording (Fig. I), the carrier is preliminarily exposed to continuous reading light beam with wavelength X, ranged into the absorption spectrum of the stable state (Br) of BR (570 nm). By this, BR converts from stable state to metastable state (M) with absorption peak at 412 nm.' The wavelength ? r of recording light is within the M-state sensitivity range. Under exposure to recording light pulse, the metastable M-state converts into the original Br-state. As a result, recorded pattern consists of spatial distributed M and Br states which have different absorption and refractive indeces.5 L. _ recordmg hologram ?Lw ii t diffracted gh 1it reading light BR Ar Fig. 1. Illustration for recording in M-state of BR SPIEVol. 3347. 0277-786X/98/$1O.OO 61 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/27/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
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