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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Convolution, Correlation, And Storage Of Optical Data In Inhomogeneously Broadened Absorbing Materials

William Randall Babbitt, Yu Bai, THOMAS W. MOSSBERG

Published Sep 24, 1986• 7 citations
Publisher

Abstract

We discuss the light signals that are coherently emitted by some optical absorbers sub-sequent to excitation by a series of three laser excitation pulses. In some cases, the light signal emitted by the material duplicates the temporal shape of one of the laser in-put pulses. In other cases, the emitted signal represents the convolution or cross-correlation of two of the laser input pulses. In principle, digitally encoded signals of multi-gigahertz bandwidth can be convolved in real time, or, in suitable materials, stored for long periods. Output signals on the order of a few percent as intense as the inputs are possible. We provide experimental demonstrations of these effects, and discuss their implementation in optical signal processing and data storage systems.

DOI
10.1117/12.964348

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We discuss the light signals that are coherently emitted by some optical absorbers sub-sequent to excitation by a series of three laser excitation pulses. In some cases, the light signal emitted by the material duplicates the temporal shape of one of the laser in-put pulses. In other cases, the emitted signal represents the convolution or cross-correlation of two of the laser input pulses. In principle, digitally encoded signals of multi-gigahertz bandwidth can be convolved in real time, or, in suitable materials, stored for long periods. Output signals on the order of a few percent as intense as the inputs are possible. We provide experimental demonstrations of these effects, and discuss their implementation in optical signal processing and data storage systems.
We have employed the recently developed technique of real-time optical waveform convolution in inhomogeneously broadened absorbers [ Appl. Phys. Lett.45, 714 ( 1984)] to perform mixed binary multiplication of digital optical signals. We demonstrate that an output signal representing the mixed binary product of up to three numbers encoded into discrete input signals can be generated in a single convolution cycle. We have studied the effect of material relaxation on output signal shapes and intensities. We find that mixed binary product signals up to ∼0.5% as intense as the input signals can be expected in weakly relaxing materials. This method of all-optical multiplication may be useful in high-speed applications, since its bit rate is limited fundamentally only by the inhomogeneous absorption bandwidth of the material used.
When a sequence of temporally modulated optical waveforms illuminate an inhomogeneously broadened absorbing medium, the resultant optical coherent transient output signal's represents the cross-correlation or convolution of the input temporal waveforms.1 The projected performance characteristics of coherent transient processors include data rates greater than 10 GHz, time-bandwidth products far in excess of 10,000, and the ability to fully process both amplitude and phase modulated waveforms.1,2 Previously it was assumed that the input data stream and pattern stream must both be shorter than the absorbing transition's homogeneous dephasing time and must both be reentered in order to process longer or multiple data streams.1 It has recently been proposed that patterns could be permanently stored in an inhomogeneously broadened solid and that input data streams of indefinite length could be continuously processed in real time without the need to reenter the input pattern.3,4 In this paper, we present a proof of concept demonstration of an optical coherent transient continuous correlator.
After the absorption profile of an inhomogeneously broadened solid is programmed by two temporally modulated pulses (at least one encoded with a pattern), it can be gated to fix the ground-state spectral population distribution permanently. The subsequent illumination of the solid by an uninterrupted, temporally modulated optical beam results in a coherent transient output signal that represents the correlation of the signal with the stored pattern. Multiple patterns can be stored at different locations on the sample and accessed randomly, enabling fast reprogramming of the processor. A performance analysis of this optical signal processor predicts that real-time continuous processing is possible with a processor bandwidth that exceeds 5 GHz, a time-bandwidth product that exceeds 10(4), and a pattern storage density that exceeds 10(5) patterns per square centimeter.