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Photonics for Computers, Neural Networks, and Memories

Frequency and time domain hybrid optical memory

Ravinder Kachru, Yu Bai, Xiao A. Shen

Published Feb 2, 1993• 0 citations
Publisher

Abstract

We describe the first experiments to validate the concept of a high-speed, high-density random access memory. This technique is based on a hybrid of the time-domain stimulated echo and the frequency domain scheme. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The advantage of the approach is the flexibility it offers in tailoring the memory system to match the computational processor. We have demonstrated storage and retrieval of data for long time in frequency bins separated by 750 MHz. We have achieved data rates of 40 MHz.

DOI
10.1117/12.983223

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Frequency and time domain hybrid optical memory

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We describe the first experiments to validate the concept of a high-speed, high-density random access memory. This technique is based on a hybrid of the time-domain stimulated echo and the frequency domain scheme. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The advantage of the approach is the flexibility it offers in tailoring the memory system to match the computational processor. We have demonstrated storage and retrieval of data for long time in frequency bins separated by 750 MHz. We have achieved data rates of 40 MHz.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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We describe the first experiments to validate the concept of a high-speed, high-density random access memory. This technique is based on a hybrid of the time-domain stimulated echo and the frequency domain scheme. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The advantage of the approach is the flexibility it offers in tailoring the memory system to match the computational processor. We have demonstrated storage and retrieval of data for long time in frequency bins separated by 750 MHz. We have achieved data rates of 40 MHz.
We describe the first experiments to validate the concept of a high-speed, high-density random access memory. This technique is based on a hybrid of the time-domain stimulated echo and the frequency domain scheme. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The advantage of the approach is the flexibility it offers in tailoring the memory system to match the computational processor. We have demonstrated storage and retrieval of data for long time in frequency bins separated by 750 MHz. We have achieved data rates of 40 MHz.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
We describe a new approach to develop a high-speed, high-density random access cache memory. This new technique is based on a novel approach using, in essence, a hybrid of the time domain stimulated echo (SE) concept and the frequency domain scheme. It has been demonstrated that the rare-earth doped crystals, can at low temperatures store large amounts of information for up to 24 hours using SE. The basic approach we have developed is the partitioning of the absorption frequency domain into smaller bins, so that each frequency bin stores a smaller portion of information independently. The bins are distinguishable by their different absorption frequencies and they are accessed by changing the laser frequency (color). However, information is still stored and retrieved using the time-domain pulse sequency used in SE. Specifically, with the laser frequency set at the particular absorption of a frequency bin, the laser is externally modulated by an acousto-optic modulator to produce amplitude modulated pulses representing the digital data, the write pulse, and the read pulse, during the write and retrieve operation, respectively. The advantages of this approach are that memory can be stored in space, time, and frequency domain, allowing us to tailor a flexible memory architecture to match those of the computational processor.
Our goal is to quantitatively evaluate the concept of time-domain optical memory (TDOM) based on the stimulated photon echo technique and to prepare for the development of a working prototype. Earlier feasibility studies at SRI International showed that TDOM can store not only digital data in the form a series of on-off laser pulses but also two-dimensional (2-D) images with the same read/write speed. Despite work at SRI and elsewhere, until now the use of TDOM for 2-D images has not been carefully examined and the quality of echo images and their inherent spatial resolution have not been explored. These issues have an important bearing on TDOM as a high-speed, high-density storage device. This year, we focused on using the stimulated echo technique for 2-D image storage and image processing. Specific tasks included incorporating a gated intensified charge-coupled device (CCD) camera system for detecting echo images, digitally recording the echo images, and optimizing the optical system. We have also extended the earlier feasibility study on stimulated-echo-based, 2- D image storage and image processing and demonstrated storage and retrieval of the high-quality, high-resolution echo images. In addition, we demonstrated for the first time that nanosecond pattern recognition can be achieved using the stimulated echo approach. (Author)
The objective of this research was to quantitatively evaluate the concept of time-domain optical memory (TDOM) using the hole-burning mechanism. The TDOM concept offers both high speed and high memory density. The advantage of TDOM over traditional semiconductor memory is its inherent parallelism, which allows data to be stored and retrieved from the memory at much higher speed. The practical success of the proposed memory, therefore, depends critically on-among other issues-the storage, retrieval, and processing of images. In addition, new data storage techniques are needed to implement a practical memory. The last three years of this research program have focused on (1) development of new phase modulation techniques to enhance the storage, retrieval, and integrity of the stored information; (2) experimental studies of image storage and phase conjugate retrieval; (3) Image processing; and (4) practical holographic storage of images by using the hybrid time-frequency approach. Specifically, SRI demonstrated data encryption by phase modulating the read and write pulses. Image correlation and convolution was demonstrated and its implication for pattern recognition examined. Finally, this laboratory demonstrated high-fidelity random access and retrieval using holographic storage in Pr3+: YA103 with a single-frequency ring laser. These experiments have clearly demonstrated the practical viability ofmore » TDOM with existing technology. In the next stage of the research, the performance Issues such as bit-error-rates, signal-to-noise ratios, and laser stability need to be addressed. Stimulated photon echoes, Optical memory, Image processing, Pattern recognition, Phase conjugation.« less
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.