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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Code division in optical memory devices based on photon echo

А. А. Калачев, Daria D. Vlasova

Published Mar 3, 2006• 0 citations
Publisher

Abstract

The theory of multi-channel optical memory based on photon echo is developed. It is shown that under long-lived photon echo regime the writing and reading of information with code division is possible using phase modulation of reference and reading pulses. A simple method for construction of a system of noise-like signals, which is based on the segmentation of Frank sequence is proposed. It is shown that in comparison to the system of random biphase signals this system leads to the efficient decreasing of mutual influence of channels and increasing of random/noise ratio under reading of information.

DOI
10.1117/12.675034

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The theory of multi-channel optical memory based on photon echo is developed. It is shown that under long-lived photon echo regime the writing and reading of information with code division is possible using phase modulation of reference and reading pulses. A simple method for construction of a system of noise-like signals, which is based on the segmentation of Frank sequence is proposed. It is shown that in comparison to the system of random biphase signals this system leads to the efficient decreasing of mutual influence of channels and increasing of random/noise ratio under reading of information.
The noise characteristics of the photon echo memory have been investigated. The photon echo memory has the ability to store many bits of information in a diffraction-limited spot, thereby dramatically increasing the storage density. The temporal Fourier transform of the input data sequence is written into the inhomogeneous absorption profile of the recording medium. Data are encoded by means of temporal modulation onto the waveform of a finite duration data beam. Individual bits are not localized to a specific spectral channel; instead, they are stored throughout a region of spectral-addressing space, In order to store and recall the input data accurately, the Fourier transform of the input data sequence must be narrower than the inhomogeneous bandwidth. In the photon echo memory mechanism, there are several factors affecting the system bit error rate such as finite-width write/read pulses, echo efficiency, shot noise, thermal noise, etc. The accuracy of the echo output depends on those system factors. In this paper we formulate a simple model of the photon echo system, and by analyzing this model we derive the relationship between the characteristics of the echo output signal and several factors such as the bandwidth of the system, echo efficiency, atom excited state population fluctuations, shot noise, and thermal noise.
The phenomenon of long-lived photon echo (LPE) has attracted much recent attention [1-6]. This interest stems from the possible application of this phenomenon in high-capacity optical memory devices (OMD) [7-8]. At present many fundamental problems crucial to the construction of an operating device are solved. The possibility of multiple information read out without refresh is shown theoretically [9] and experimentally [5,10]. Resonant media with storage times of the order of tens of hours and more have been investigated [4,5].Nevertheless, up to now it has not been clear whether it is possible to selectively erase information in an arbitrary memory cell of OMD. It was pointed out for the first time in Ref. [ 11] that it is in principle possible to erase information with random access using LPE signal suppression. We investigate the effect of LPE signal suppression in this work in more detail, and propose a simple technique for random access information erasing.