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Journal of the Optical Society of America B

Influence of laser phase and frequency fluctuations on photon-echo data erasure

Ulf Elman, Baozhu Luo, Stefan Kröll

Published Sep 1, 1996• 18 citations
Publisher

Abstract

Erasure of data stored by use of photon echoes has been investigated as a function of data writing time and data storage time. The results clarify the requirements on laser phase and frequency stability for performing photon-echo data erasure. The analysis of phase and frequency stability of a light source by the photon-echo erasure process is illustrated. A theoretical analysis emphasizing the physical processes that affect the erasure efficiency as well as an extensive discussion of possible error sources are given. Finally, an approach to bit-selective photon-echo data erasure that is insensitive to laser phase and frequency fluctuations is suggested.

DOI
10.1364/josab.13.001905

Related papers

The effect of laser frequency and phase fluctuations on coherent addition and erasure of photon echoes

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One important possible application of photon echoes is all-optical data storage. Photon echoes have a number of advantageous properties that make diem very good candidates for such applications, such as high areal density (1 Tb/cm2 has been projected [1], which should be compared with approximately 1 Mb/cm2 for commercially available CMOS memories today) and readout speeds >THz have been experimentally demonstrated [2]. We have addressed the problem of how to selectively erase data bits stored using photon echoes. One solution to this problem is to coherently add a new echo, phase shifted 180 degrees relative to the original echo, and thus achieve selective erasure of data [3].

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An investigation is made of the efficiency of repeated excitation of a sample by laser pulse pairs when data are stored by the photon echo method. Fluctuations of the difference between the pulse phases in different pairs, resulting from instability of the optical path length in the delay line, are shown to prevent cophasal superposition of a set of level-population gratings. The possibility of weakening the negative influence of this effect on the intensity of the read echo signal is considered.

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Bit error rates for a photon echo memory

Jin Y. Choi, John F. Walkup, Thomas F. Krile +1 more

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.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 5, 1998•1 citation
Erasure of data stored by use of photon echoes has been investigated as a function of data writing time and data storage time. The results clarify the requirements on laser phase and frequency stability for performing photon-echo data erasure. The analysis of phase and frequency stability of a light source by the photon-echo erasure process is illustrated. A theoretical analysis emphasizing the physical processes that affect the erasure efficiency as well as an extensive discussion of possible error sources are given. Finally, an approach to bit-selective photon-echo data erasure that is insensitive to laser phase and frequency fluctuations is suggested.
One important possible application of photon echoes is all-optical data storage. Photon echoes have a number of advantageous properties that make diem very good candidates for such applications, such as high areal density (1 Tb/cm2 has been projected [1], which should be compared with approximately 1 Mb/cm2 for commercially available CMOS memories today) and readout speeds >THz have been experimentally demonstrated [2]. We have addressed the problem of how to selectively erase data bits stored using photon echoes. One solution to this problem is to coherently add a new echo, phase shifted 180 degrees relative to the original echo, and thus achieve selective erasure of data [3].
Photon echoes have been studied both experimentally and theoretically, with the main part of the work centred around the concept of using photon echoes for all-optical data storage and processing. The four basic Boolean operators, AND, OR, NOT and XOR have been experimentally demonstrated using photon echoes. These constitute a complete set of Boolean operators. Selective erasure of digital data bits stored using photon echoes have been performed experimentally using three different laser systems with increasing frequency stabilities spanning three orders of magnitude, and the demands put on laser phase- and frequency stability using the suggested erasure method, have been studied. The effects of laser phase- and frequency fluctuations on both ordinary stimulated echoes and on coherently added echoes, have been analysed theoretically using the theory of stochastic processes. The resulting bit error rates in digital optical data processing systems due to such fluctuations have been considered. It has been shown possible experimentally to amplify photon echoes using fibre amplifiers, and to regenerate echoes from echoes amplified with this method. The advantages and limitations of this method for regeneration of photon echoes have been studied.
The effect of random laser phase fluctuations on stimulated photon echoes (SPEs) and on coherently added SPEs was studied and evaluated both experimentally and analytically with statistical methods. The general concept of describing laser frequency fluctuations as a stationary stochastic process is presented and applied to three specific SPE configurations. The effect of phase fluctuations on erasing an SPE by coherently adding another SPE, phase-shifted by 180 degrees relative to the first, is presented.
Time-and-space-domain holography [1,2] by stimulated photon echoes [3] provides a means of storing temporal and spatial properties of an ultrafast-varying light signal and recalling its authentic replica at any later moment. The possibility of recording complex time shapes of light pulses, which also means time-domain optical data storage, is based on the ability of frequency-selective absorbers to store with high accuracy the temporal Fourier components of the incident light [1-3]. The time-domain frequency-selective optical storage of binary or analog data is an alternative approach to the concept of frequency-selective high-density data storage that provides a parallel ultrafast data storage and processing in the frequency domain. The shortest detail of the signal to be stored is limited by the reverse inhomogeneous bandwidth of the storing media which reaches 10-100 fs for frequency-selective materials while the duration of the signal is limited by phase relaxation time T2 (usually 10−9-10−6s).
An investigation is made of the efficiency of repeated excitation of a sample by laser pulse pairs when data are stored by the photon echo method. Fluctuations of the difference between the pulse phases in different pairs, resulting from instability of the optical path length in the delay line, are shown to prevent cophasal superposition of a set of level-population gratings. The possibility of weakening the negative influence of this effect on the intensity of the read echo signal is considered.
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.