This report summarizes the results of a 3-year program of research on the physics and technology needed to develop high-performance optical memory and optical processing systems based on the concept called the stimulated photon echo (SPE). The research goals were investigation, demonstration, and improvement of signal strength and fidelity, architectures and algorithms, and materials properties for optical storage and in-memory processing. Key accomplishments were (1) development and demonstration of efficient algorithms for threshold discrimination and bit-error-rate reduction in retrieved binary images with large in-frame and frame-to-frame intensity variations; (2) demonstration and characterization of information storage in Erbium-doped crystals using 1.5-micron diode lasers compatible with fiber optic communications; (3) demonstration of improved phase-encoding schemes for in-memory temporal correlation of 1.5-micron pulse trains; (4) development of concepts for high-performance radar applications based on SPE optical memory for time-delay control of the transmitter array and in-memory image processing of the return signals; and (5) hosting the AFOSR Contractors' Meeting, "Optoelectronic Information Processing."
This report summarizes the results of a 3-year program of research on the physics and technology needed to develop high-performance optical memory and optical processing systems based on the concept called the stimulated photon echo (SPE). The research goals were investigation, demonstration, and improvement of signal strength and fidelity, architectures and algorithms, and materials properties for optical storage and in-memory processing. Key accomplishments were (1) development and demonstration of efficient algorithms for threshold discrimination and bit-error-rate reduction in retrieved binary images with large in-frame and frame-to-frame intensity variations; (2) demonstration and characterization of information storage in Erbium-doped crystals using 1.5-micron diode lasers compatible with fiber optic communications; (3) demonstration of improved phase-encoding schemes for in-memory temporal correlation of 1.5-micron pulse trains; (4) development of concepts for high-performance radar applications based on SPE optical memory for time-delay control of the transmitter array and in-memory image processing of the return signals; and (5) hosting the AFOSR Contractors' Meeting, "Optoelectronic Information Processing."
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
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.
Optical memories based on spectral hole burning (SHB) and stimulated photon echoes (SPE) are attracting much attention. Both approaches add an extra dimension for addressing (frequency and temporal dimension respectively) to the spatial dimensions. With these concepts the storage density can become 103 – 106 times higher than in conventional optical memories. In both approaches, the ratio of the inhomogeneous line width to the homogeneous line width of the ions activated in the storage process determines the improvement in storage density. Compared to the SHB approach, SPE has certain advantages including high R/W rate and ability to process the stored (spatial as well we temporal) information. Using SPE, the authors have experimentally realised the AND, OR and NOT logical operations [1,2]. Further all optical processing, such as temporal pattern recognition, can be done using SPE.
Abstract : Optical materials for spectral hole burning and coherent transient applications were designed and evaluated, emphasizing relevance to devices including high performance memory, signal processing, high speed holographic recording and analysis, and optical switches, routers, and buffers. The ultimate limits on material performance set by atomic mechanisms were determined. The developed materials contained Eu3+, Pr3+, Tm3+, Tb3+, or Er3+ active ions in various oxide hosts. The first report was made of an Er3+ material for hole burning applications in 1.5 micron optical communications bands. Eight Er3+ materials for applications at 1.5 microns in optical routers and buffer memories were designed and characterized. A correlator' signal processing capability was demonstrated, and the first report was made of operation of a 1.5 micron packet header decoder for all-optimized optical packet switching in optical communications along optical fibers at 1531 nm. Eu3+:Y2SiO5 was optimized for use in 100 GByte ODRAM optical memory devices, considering Eu3+ concentration and temperature. Eight Tm3+ compounds for signal processing applications, such as true time delays for phased-array radar, at diode laser wavelengths near 795 nm were designed and characterized. Eight Tb3+ compounds for photon gated spectral hole burning were designed and characterized, and gated hole burning was observed in Tb3+:YAIO3.