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Optics Letters

Optical correlator that uses cesium vapor

Ivan Biaggio, B. Ai, R. J. Knize, Jouni P. Partanen, R. W. Hellwarth

Published Nov 1, 1994• 5 citations
Publisher

Abstract

We obtain the correlation pattern between two amplitude-modulated input images of 36 and 280 random black and white pixels, using the standard degenerate four-wave-mixing geometry of 852-nm optical beams in a 1-mm-thick cesium-vapor cell. The total optical input power is 3.2 mW to obtain 0.4 nW of power in the correlation pattern. We verified that the buildup time of the four-wave-mixing signal is ~30 ns. Using the random patterns, we analyze the performance of the cesium optical correlator in terms of the number of pixels that can be processed and the number of photons per pixel used. We show how to scale our experimental results for the efficiency of the cesium correlator to images containing a larger number of pixels.

DOI
10.1364/ol.19.001765

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We obtain the correlation pattern between two amplitude-modulated input images of 36 and 280 random black and white pixels, using the standard degenerate four-wave-mixing geometry of 852-nm optical beams in a 1-mm-thick cesium-vapor cell. The total optical input power is 3.2 mW to obtain 0.4 nW of power in the correlation pattern. We verified that the buildup time of the four-wave-mixing signal is ~30 ns. Using the random patterns, we analyze the performance of the cesium optical correlator in terms of the number of pixels that can be processed and the number of photons per pixel used. We show how to scale our experimental results for the efficiency of the cesium correlator to images containing a larger number of pixels.
Nondegenerate four-wave mixing (FWM) in diamond-type atomic systems has important applications in a wide range of fields, including quantum entanglement generation, frequency conversion, and optical information processing. Although the efficient self-seeded nondegenerate FWM with amplified spontaneous emission (ASE) has been realized extensively, the seeded nondegenerate FWM without ASE is inefficient in reported experiments so far. Here we present the experimental realization of the seeded nondegenerate FWM in cesium atoms with a significantly improved efficiency. Specifically, with two pump lasers at 852 and 921 nm and a seed laser at 895 nm, a continuous-wave laser at 876 nm is efficiently generated via FWM in a cesium vapor cell with a power up to 1.2 mW, three orders of magnitude larger than what has been achieved in previous experiments. The improvement of the efficiency benefits from the exact satisfaction of the phase-matching condition realized by an elaborately designed setup. Our results may find applications in the generation of squeezing and entanglement of light via nondegenerate FWM.
Abstract : This project examined the use of atomic vapors in an optical correlator for pattern recognition. The nonlinear optics of very thin atomic vapors was studied. This work allowed the demonstration of an optical correlator in a thin cesium vapor. This correlator was able to compare patterns of letters as well as random patterns. The patterns can contain up to 10 to the 5th power pixel/cm2 and the correlation is obtained in 10 microseconds. In addition, methods to improve the performance of the optical correlator were investigated. Experiments showed that motion of the atoms during the excited state lifetime of 30 nsec limited the smallest pixel size to about 30 microns. Two methods that were investigated to improve this resolution were the use of buffer gasses to confine the atoms and laser cooling the atoms to reduce their speed. One set of experiments showed that buffer gasses can either quench the excited state lifetime or limited diffusion of the excited state atoms. Another set of experiments began investigation of laser cooling techniques to slow the atomic motion.
We have built a compact light source for bright squeezed twin-beams at 795\,nm based on four-wave-mixing in atomic 85^{85}85Rb vapor. With a total optical power of 400\,mW derived from a free running diode laser and a tapered amplifier to pump the four-wave-mixing process, we achieve 2.1\,dB intensity difference squeezing of the twin beams below the standard quantum limit, without accounting for losses. Squeezed twin beams generated by the type of source presented here could be used as reference for the precise calibration of photodetectors. Transferring the quantum correlations from the light to atoms in order to generate correlated atom beams is another interesting prospect. In this work we investigate the dispersion that is generated by the employed four-wave-mixing process with respect to bandwidth and dependence on probe detuning. We are currently using this squeezed light source to test the transfer of spatial information and quantum correlations through media of anomalous dispersion.
We demonstrate the generation of polychromatic and collimated lights at 456 nm, 459 nm, and 761 nm based on cesium ( 133 Cs) 6S 1/2 - 6P 3/2 - 8S 1/2 - 7P 3/2 , 7P 1/2 , 6P 1/2 - 6S 1/2 multi-diamond-type atomic system via two-photon excitation with two IR pump lasers at 852 nm and 795 nm. The 456 nm, 459 nm (7P 3/2 , 7P 1/2 → 6S 1/2 ) collimated blue lights result from the self-seeded four-wave mixing process (FWM), and the 761 nm coherent light (8S 1/2 → 6P 1/2 ) is from a seeded FWM process with the injection of a third laser at 895 nm. We measure the dependency of generated polychromatic fields on the temperature of 133 Cs vapor cell and the powers of input lasers, clearly demonstrating the competition between the self-seeded FWM and seeded FWM, as they share the same excitation path. This work is helpful to further produce entangled multi-color photons for quantum communication.
We present experimental results showing that quantum correlated light can be produced using non-degenerate, off-resonant, four-wave mixing (4WM) on both the D1 (795 nm) and D2 (780 nm) lines of (85)Rb and (87)Rb, extending earlier work on the D1 line of (85)Rb. Using this 4WM process in a hot vapor cell to produce bright twin beams, we characterize the degree of intensity-difference noise reduction below the standard quantum limit for each of the four systems. Although each system approximates a double-lambda configuration, differences in details of the actual level structure lead to varying degrees of noise reduction. The observation of quantum correlations on light produced using all four of these systems, regardless of their substructure, suggests that it should be possible to use other systems with similar level structures in order to produce narrow frequency, non-classical beams at a particular wavelength.