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Optics Letters

Nanosecond image processing using stimulated photon echoes

E. Y. Xu, M. K. Kim, Stefan Kröll, David L. Huestis, Ravinder Kachru

Published Mar 26, 1990• 35 citations
Publisher

Abstract

Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal (0.1 at. % Pr(3+):LaF(3)). Two spatially encoded laser pulses (pictures) resonant with the (3)P(0)-(3)H(4) transition of Pr(3+) were stored by focusing the image pulses sequentially into the Pr(3+):LaF(3) crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed.

DOI
10.1364/ol.15.000562

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Apr 1, 1992•2 citations
Processing of two-dimensional images on a nanosecond time scale is demonstrated using the stimulated photon echoes in a rare-earth-doped crystal (0.1 at. % Pr(3+):LaF(3)). Two spatially encoded laser pulses (pictures) resonant with the (3)P(0)-(3)H(4) transition of Pr(3+) were stored by focusing the image pulses sequentially into the Pr(3+):LaF(3) crystal. The stored information is retrieved and processed by a third read pulse, generating the echo that is the spatial convolution or correlation of the input images. Application of this scheme to high-speed pattern recognition is discussed.
We present experimental results demonstrating the use of stimulated echoes for high-speed pattern recognition. One data image and two reference images (spatially encoded laser pulses) were stored and processed in a Pr(3+):LaF(3) crystal by focusing the pulses sequentially into the storage material. The processed information was later retrieved by a read pulse, generating two temporally separated echo images that are the spatial correlations between the data and reference images. Identification of the data image was accomplished by finding the echo image that showed the highest spatial correlation with the data image. The present processing speed is 30 ns per correlation operation.
We demonstrate, we believe for the first time, the capability of spatial pattern recognition by backward stimulated photon echo (BSPE) in a low temperature solid activated by rare earth ions. The BSPE experiment is done with three time-delayed input laser pulses. The first pulse (DATA) contains several characters in its beam profile, the second pulse (WRITE) is a plane wave, and the third (READ) has the search character. The echo pulse profile has peak intensity at the position of the search character. The experiment has a time scale of several tens of nanoseconds. Pattern recognition by BSPE is a result of the convolution/correlation property of holographic four-wave mixing geometry. In contrast to the photorefractive processes, however, the BSPE in rare earth-doped solids is a resonant coherent optical transient effect. By combining spatial and temporal holographic processes of BSPE, it would be possible to construct a high density, high speed optical processor of spatial and temporal data using BSPE.
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)
We demonstrate mixed binary multiplication of two or three numbers represented as spatial bit patterns by using a backward stimulated photon echo in a low-temperature solid activated by rare-earth ions. The photon-echo output image is the convolution-correlation of input images in a holographic arrangement, which can be interpreted as multiplication in a mixed binary format. The computation is extremely fast (~ 50 ns) and may be combined with temporal data processing for a versatile vector and matrix processor.
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.