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Molecular crystals and liquid crystals science technology. Section A, Molecular crystals and liquid crystals/Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals

Time-Domain Optical Memory in Hole-Burning Materials

Ravinder Kachru, Xiao A. Shen, Yu Bai

Published Aug 1, 1994• 2 citations
Publisher

Abstract

We have demonstrated storage of 2 Kbits of data at 40 Mbits/s in the Eu3+ doped Y2SiO5 crystal using the time-domain echo approach. Preventing coherent saturation, caused by the long data pulse train, is critical to the successful implementation of this technique. The experimentally inferred storage capacity of 6 × 104 spatial spot demonstrates the potential of this optical memory.

DOI
10.1080/10587259408038226

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We report time-domain data storage of as much as 1.6 kbits at a rate of 40 Mbits/s in Eu3+:YOS. Use of a pseudorandom biphase shifting technique to spread the data spectrum proved to be of critical importance in preventing saturation of the transition by the long data pulse train. The experimentally inferred storage capacity, ≳ 5 × 104 bits/spatial spot, plus the competitive single-channel throughput rate, demonstrate the potential of this optical memory.

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The photon-echo memory[1], or the time-domain optical data storage, resembles the hole-burning memory [2] in that the inhomogeneous absorption line of a material is employed as a storage medium and the information is stored in it as a frequency-dependent absorption change with the resolution determined by the homogeneous width. Having the common memory capacity N given by the inhomogeneous-to-homogeneous width ratio, both types of memories share common problems like low-temperature operation, spectral diffusion and so on. Although a storage medium is common, storage techniques are definitely different for the two memories. The photon-echo memory utilizes the temporal interference effect between a reference pulse and a data pulse and their interference pattern is stored as a population grating in the frequency domain. In this sense this is a time-domain analog of holography where the spatial interference pattern between a reference beam and a data beam is stored in a medium as a population grating in the real space. Like the spatially diffracted beam from the read beam gives the information stored in the hologram, the “temporally diffracted pulse", or the photon echo, after the read pulse can give the information stored in the inhomogeneous distribution.

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Optical Memories and Processing in Time- and Frequency Domain

Baozhu Luo

Spectral hole burning and photon echoes are the techniques for frequency-selective optical memories, which have the potential to increase areal data storage density by a factor 10**7. They also have the capability to perform in-memory data processing. In this thesis, several materials and techniques for optical memories in the frequency- and time domain have been investigated. In the frequency domain, ways to increase the storage density and the working temperature were studied using photon-gated spectral hole burning materials of the metal-tetrabenzoporphyrin derivatives. A selection rule for the electron acceptors in the donor-acceptor electron transfer systems was deduced. By doping the material with two different donors a maximum inhomogeneous line width of more than 30 THz was achieved. A polarization holographic technique was established for the formation and detection of spectral holes. Our results indicate that this technique can provide a better signal-to-noise ratio than that achieved by a conventional holographic technique, in particular for samples of poor optical quality. In the time domain, magnetic field-induced and the intensity-induced dephasing processes were studied in Pr3+ doped in a YAlO3 crystal and a Y2SiO5 crystal, respectively. As a step along the route to make photon echo based optical processing possible, the amplification of photon echo signals by the use of a fiber amplifier (Pr3+-doped ZBLAN) was demonstrated. A gain of 45 was achieved. The erasure of stored data using photon echoes has also been investigated. A technique to diagnose the phase and frequency stability of a light source by the photon echo erasure process was proposed and illustrated. An approach to bit-selective data erasure, that is free from laser phase and frequency fluctuations, is also suggested. A concept for an arbitrary shape pulse generator based on photon echoes and hole-burning was experimentally and theoretically studied. Finally, a comparison between the properties and capabilities of spectral hole burning and photon echoes was made.

Lund reports on atomic physics•Jan 1, 1998•0 citations

Multiple-Bit Long-Term Data Storage by Backward Stimulated Echo in eu3+:yalo3

M. K. Kim, Ravinder Kachru

The backward stimulated echo has been considered as a novel high-speed high-density optical data storage method. But its potential application has been confined to transient dynamic memory because of relatively short lifetime of optical coherence inside low-temperature solids. Here we report the longest observed storage time of at least six hours in the 581.8 nm7F0-5D0 transition of eu 3+ -doped YAlO3 crystal at 2°K. The experiments are performed using YAG-pumped pulsed dye lasers, beamsplitters and optical delay lines to produce five DATA pulses, at 20 nsec intervals, and WRITE and READ pulses. The measured echo intensity as a function of storage time has exponential decay time of 3.8 hours. This very long storage time is due to the very small effective nuclear magnetic moments of Eu3+ ions, and is consistent with the long lifetime of spectral hole in this system. We also observed that the signal fidelity is not noticeably affected by the number of DATA pulses and the long storage time.

Annual Meeting Optical Society of America•Jan 1, 1988•0 citations
We have demonstrated storage of 2 Kbits of data at 40 Mbits/s in the Eu3+ doped Y2SiO5 crystal using the time-domain echo approach. Preventing coherent saturation, caused by the long data pulse train, is critical to the successful implementation of this technique. The experimentally inferred storage capacity of 6 × 104 spatial spot demonstrates the potential of this optical memory.
The photon-echo memory[1], or the time-domain optical data storage, resembles the hole-burning memory [2] in that the inhomogeneous absorption line of a material is employed as a storage medium and the information is stored in it as a frequency-dependent absorption change with the resolution determined by the homogeneous width. Having the common memory capacity N given by the inhomogeneous-to-homogeneous width ratio, both types of memories share common problems like low-temperature operation, spectral diffusion and so on. Although a storage medium is common, storage techniques are definitely different for the two memories. The photon-echo memory utilizes the temporal interference effect between a reference pulse and a data pulse and their interference pattern is stored as a population grating in the frequency domain. In this sense this is a time-domain analog of holography where the spatial interference pattern between a reference beam and a data beam is stored in a medium as a population grating in the real space. Like the spatially diffracted beam from the read beam gives the information stored in the hologram, the “temporally diffracted pulse", or the photon echo, after the read pulse can give the information stored in the inhomogeneous distribution.
We propose and demonstrate a novel type of frequency-selective optical memory that writes and reads the data in both the time domain and the frequency domain. Temporal 16-bit data were stored by accumulated-photon-echo bit-by-bit storage at 103 frequency addresses within the inhomogeneous line of the (7)F(0)-(5)D(0) transition of Eu(3+):Y(2)SiO(5), which yields a total memory capacity of 1.6 kbits in a single spot of 240-microm diameter. The keys to the success of this experiment are this material's long dephasing time and lack of spectral diffusion.
Spectral hole burning and photon echoes are the techniques for frequency-selective optical memories, which have the potential to increase areal data storage density by a factor 10**7. They also have the capability to perform in-memory data processing. In this thesis, several materials and techniques for optical memories in the frequency- and time domain have been investigated. In the frequency domain, ways to increase the storage density and the working temperature were studied using photon-gated spectral hole burning materials of the metal-tetrabenzoporphyrin derivatives. A selection rule for the electron acceptors in the donor-acceptor electron transfer systems was deduced. By doping the material with two different donors a maximum inhomogeneous line width of more than 30 THz was achieved. A polarization holographic technique was established for the formation and detection of spectral holes. Our results indicate that this technique can provide a better signal-to-noise ratio than that achieved by a conventional holographic technique, in particular for samples of poor optical quality. In the time domain, magnetic field-induced and the intensity-induced dephasing processes were studied in Pr3+ doped in a YAlO3 crystal and a Y2SiO5 crystal, respectively. As a step along the route to make photon echo based optical processing possible, the amplification of photon echo signals by the use of a fiber amplifier (Pr3+-doped ZBLAN) was demonstrated. A gain of 45 was achieved. The erasure of stored data using photon echoes has also been investigated. A technique to diagnose the phase and frequency stability of a light source by the photon echo erasure process was proposed and illustrated. An approach to bit-selective data erasure, that is free from laser phase and frequency fluctuations, is also suggested. A concept for an arbitrary shape pulse generator based on photon echoes and hole-burning was experimentally and theoretically studied. Finally, a comparison between the properties and capabilities of spectral hole burning and photon echoes was made.
The backward stimulated echo has been considered as a novel high-speed high-density optical data storage method. But its potential application has been confined to transient dynamic memory because of relatively short lifetime of optical coherence inside low-temperature solids. Here we report the longest observed storage time of at least six hours in the 581.8 nm7F0-5D0 transition of eu 3+ -doped YAlO3 crystal at 2°K. The experiments are performed using YAG-pumped pulsed dye lasers, beamsplitters and optical delay lines to produce five DATA pulses, at 20 nsec intervals, and WRITE and READ pulses. The measured echo intensity as a function of storage time has exponential decay time of 3.8 hours. This very long storage time is due to the very small effective nuclear magnetic moments of Eu3+ ions, and is consistent with the long lifetime of spectral hole in this system. We also observed that the signal fidelity is not noticeably affected by the number of DATA pulses and the long storage time.