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IEEE International Conference on Rebooting Computing (ICRC)

Spatial-Spectral Materials for High Performance Optical Processing

Zeb W. Barber, Calvin C. Harrington, Krishna Rupavatharam, Charles W. Thiel, Trent Jackson, Peter B. Sellin, Craig Benko, K.D. Merkel

Published Nov 1, 2017• 1 citation
Publisher

Abstract

Optically active Spatial-Spectral (S2) materials are a unique resource for spectrally based optical memory and processing. At cryogenic temperatures, the rare-earth ions in these materials individually exhibit narrow optical resonances on the order of MHz to sub-KHz, but are inhomogeneously broadened over GHz to THz spectral bandwidths providing up to 107resolvable spectral channels. The material can be optically programmed to transform the spectral and spatial components of optical signals to perform signal processing operations such analog multiplications, time delay, filtering, convolutions, and correlations. We present work utilizing the S2 technology for high bandwidth (>32 GHz) and data rate selection and filtering, including processing of 1D data streams in real-time and 2D images. Despite cryogenic cooling, the power efficiency of the S2 technology compares favorably to CMOS in large scale systems. Finally, potential architectures for large (106× 106) vector-matrix multipliers using S2 materials are discussed.

DOI
10.1109/icrc.2017.8123674

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Optically active Spatial-Spectral (S2) materials are a unique resource for spectrally based optical memory and processing. At cryogenic temperatures, the rare-earth ions in these materials individually exhibit narrow optical resonances on the order of MHz to sub-KHz, but are inhomogeneously broadened over GHz to THz spectral bandwidths providing up to 107resolvable spectral channels. The material can be optically programmed to transform the spectral and spatial components of optical signals to perform signal processing operations such analog multiplications, time delay, filtering, convolutions, and correlations. We present work utilizing the S2 technology for high bandwidth (>32 GHz) and data rate selection and filtering, including processing of 1D data streams in real-time and 2D images. Despite cryogenic cooling, the power efficiency of the S2 technology compares favorably to CMOS in large scale systems. Finally, potential architectures for large (106× 106) vector-matrix multipliers using S2 materials are discussed.
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Many storage and processing systems based on spectral holeburning have been proposed that access the broad bandwidth and high dynamic range of spatial-spectral materials, but only recently have practical systems been developed that exceed the performance and functional capabilities of electronic devices. This paper reviews the history of the proposed applications of spectral holeburning and spatial-spectral materials, from frequency domain optical memory to microwave photonic signal processing systems. The recent results of a 20 GHz bandwidth high performance spectrum monitoring system with the additional capability of broadband direction finding demonstrates the potential for spatial-spectral systems to be the practical choice for solving demanding signal processing problems in the near future.
Recent years have seen the development of a variety of techniques for the storage and processing of optical data streams in materials with [1-10] and without [11-12] intrinsic frequency selectivity. These techniques are characterized by very high bandwidth and relatively large time-bandwidth product. It is known, that the optical processes responsible for the storage and/or processing of temporal waveform data frequently also lead to the storage of spatial waveform information [13,14]. It has been demonstrated, for example, that sequences of images can be stored. [5,7,8] An area that is relatively unexplored, however, relates to the possible interactions between stored temporal and spatial information. We explore one example of how the temporal and spatial information stored within a material can interact and lead to a novel functionality, i. e. the passive routing of optical beams along one of many possible temporally encoded directions.
We propose a novel, wideband spectrum analyzer based on spectral hole burning (SHB) technology. SHB crystals contain rare earth ions doped into a host lattice, and are cooled to cryogenic temperatures to allow sub-MHz hole burning linewidths. The signal spectrum is recorded in an SHB crystal by illuminating the crystal with an optical beam modulated by the RF signal of interest. The signal's spectral components excite those rare earth ions whose resonance frequencies coincide with the spectral component frequencies, engraving the RF spectrum into the crystal's absorption profile. Probing this altered absorption profile with a low power, chirped laser while measuring the transmitted intensity results in a time-domain readout of the accumulated RF signal spectrum. The resolution of the spectrum analyzer is limited only by the homogeneous linewidth of the rare earth ions (< 1 MHz when the SHB crystal is cooled to cryogenic temperatures). The spectrum analyzer bandwidth is limited by the inhomogeneous linewidth and by the electro-optic modulator bandwidth, both of which can be > 20 GHz.