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

Bit error rates for a photon echo memory

Jin Y. Choi, John F. Walkup, Thomas F. Krile, David J. Mehrl

Published Nov 5, 1998• 1 citation

Abstract

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.

DOI: 10.1117/12.330424

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The photon echo memory is one of the most attractive optical memories in terms of memory capacity and access speed. Fundamentally, the storage capacity and access speed are limited by the inhomogeneous bandwidth of the material. In reality, however, the storage capacity and data rates are further limited by several kinds of imperfections in the memory process. One of the main limiting factors is the noise caused by several sources. In this dissertation we categorize these noise sources into three groups, time domain noise, frequency domain noise, and detection noise. For each noise group, we create models and characterize the noise properties. We then simulate each noise model in the computer and compare the results with the analytical results. Experimental results are also presented. Those experimental results yield insight into the photon echo memory system and its physical noise characteristics. The dissertation concludes with an interpretation of the noise modeling approach described and proposes fiiture directions for this research area.

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