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Physical Review A

Quantum noise reduction in optical imaging: Role of the spatial coherence of the source

Mikhail I. Kolobov

Published Feb 1, 1995• 3 citations
Publisher

Abstract

Quantum fluctuations in image irradiance for spatially partially coherent optical imaging are studied as a function of the spatial coherence of the source. The advantage of using incoherent or partially coherent illumination for the quantum noise performance is discussed. The results are compared for illumination by coherent, spatially single-mode squeezed, and spatially multimode squeezed light. It is shown that a signal-to-noise ratio can be improved beyond the shot-noise limit employing the two latter sources.

DOI
10.1103/physreva.51.1656

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Quantum fluctuations in image irradiance for spatially partially coherent optical imaging are studied as a function of the spatial coherence of the source. The advantage of using incoherent or partially coherent illumination for the quantum noise performance is discussed. The results are compared for illumination by coherent, spatially single-mode squeezed, and spatially multimode squeezed light. It is shown that a signal-to-noise ratio can be improved beyond the shot-noise limit employing the two latter sources.
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We numerically investigate the role of quantum fluctuations in superresolution of optical objects. First, we confirm that when quantum fluctuations are not taken into account, one can easily improve the resolution by one order of magnitude beyond the diffraction limit. Then we investigate the standard quantum limit of superresolution which is achieved for illumination of an object by a light wave in a coherent state. We demonstrate that this limit can be beyond the diffraction limit. Finally, we show that further improvement of superresolution beyond the standard quantum limit is possible using the object illumination by a multimode squeezed light.
For more than a century, the diffraction limit has defined the resolution achievable by passive optical imaging systems. Although some resolution improvement can be gained through classical data processing of the image, it is limited by the noise arising from quantum nature of light. Minimizing the effect of this noise requires quantum treatment of optical imaging. By reformulating imaging as a problem of quantum measurement and estimation, it becomes possible to identify optimal detection strategies that recover spatial information previously thought inaccessible. This review summarizes the theoretical framework that underpins this development, from the formulation of quantum Cramer-Rao bounds and Chernoff bounds to the construction of receivers that attain them, such as those based on spatial-mode demultiplexing. We show how these methods can beat conventional imaging in the classification, localization, and imaging of sub-Rayleigh incoherent sources. We then discuss extensions to multiparameter and partially coherent scenarios, and highlight the unifying connections between estimation and discrimination tasks. Finally, we survey recent experimental demonstrations that approach quantum-limited resolution and outline emerging applications in microscopy, astronomy, and optical sensing.