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Optics Letters

Super-resolution imaging by anticorrelation of optical intensities

Shao-Ying Meng, Ying-Hui Sha, Qiang Fu, Qianqian Bao, Weiwei Shi, Guodong Li, Xi-Hao Chen, Ling-An Wu

Published Sep 24, 2018• 13 citations
Publisher

Abstract

Photon bunching, a feature of classical thermal fields, has been widely exploited to implement ghost imaging. Here we show that spatial photon antibunching can be experimentally observed via low-pass filtering of the intensities of the two thermal light beams from a beamsplitter correlation system. Through suitable choice of the filter thresholds, the minimum of the measured normalized anti-correlation function, i.e., antibunching dip, can be lower than 0.2, while its full-width-at-half-maximum can be much narrower than that of the corresponding positive correlation peak. Based on this anti-correlation effect, a super-resolution negative ghost image is achieved in a lensless scheme, in which the spatial resolution can exceed the Rayleigh diffraction limit by more than a factor of two. The setup is quite simple and easy to implement, which is an advantage for practical applications.

DOI
10.1364/ol.43.004759

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Photon bunching, a feature of classical thermal fields, has been widely exploited to implement ghost imaging. Here we show that spatial photon antibunching can be experimentally observed via low-pass filtering of the intensities of the two thermal light beams from a beamsplitter correlation system. Through suitable choice of the filter thresholds, the minimum of the measured normalized anti-correlation function, i.e., antibunching dip, can be lower than 0.2, while its full-width-at-half-maximum can be much narrower than that of the corresponding positive correlation peak. Based on this anti-correlation effect, a super-resolution negative ghost image is achieved in a lensless scheme, in which the spatial resolution can exceed the Rayleigh diffraction limit by more than a factor of two. The setup is quite simple and easy to implement, which is an advantage for practical applications.
Spatial anti-bunching, in contrast to the well-known bunching behavior observed in classical light sources, describes a situation where photons tend to avoid each other in space, resulting in a reduced probability of detecting two or more photons in proximity. This anti-bunching effect, a hallmark of nonclassical light, signifies a deviation from classical intensity fluctuations and has been observed not only in free electrons and entangled photon pairs but also in chaotic-thermal light. This work investigates the generation mechanism of spatial anti-bunching correlation in random light fields, leveraging the wandering of light centers to induce a second-order coherence degree below unity. Unlike traditional Gaussian Schell-model partially coherent light, this work predicts the emergence of two fundamentally distinct orbital angular momentum states, arising from the inherent differences between rigid body rotation and fluid-like rotation in the wandering light. These predictions are supported by experimental evidence. Based on these findings, we propose a resolution-enhanced lensless ghost imaging system as an application example. Experimental results indicate that the adoption of the anti-bunching correlated light field as the illumination source enables the imaging system to attain super-resolution imaging capabilities. Our findings provide new insights into the utilization of anti-correlated light fields for precision imaging and detection applications.
High-resolution ghost image and ghost diffraction are performed by using a single source of pseudo-thermal speckle light divided by a beam splitter. By only operating on the optical setup of the light in the reference arm, that never interacted with the object, we are able to pass from the image to the diffraction pattern. The product of spatial resolutions of the ghost image and ghost diffraction experiments is shown to overcome a limit which was formerly thought to be achievable only with entangled photons. A complementarity between the spatial coherence of the beams and their mutual correlation is demonstrated by showing a complementarity between ghost diffraction and ordinary diffraction patterns.
Optical intensity correlation is a fundamental property of light and an essential resource for numerous optical applications. In this work, we introduce the concept of classical correlation swapping, a classical analogue of quantum entanglement swapping, to generate all-purpose spatial correlations between two independent thermal light sources. Using a spatially unresolved Mach-Zehnder interferometer and a medium variable, we theoretically and experimentally demonstrate the feasibility of the correlator with two distinct schemes for independent pseudo-thermal light beams. Notably, the resulting photon correlations can be readily tailored to exhibit either bunching (peak) or anti-correlated (dip) characteristics, with a significantly reduced number of post-selection measurements. Leveraging this classical correlator, we further demonstrate the first classical ghost imaging experiment using uncorrelated or unknown light. Numerical simulations also confirm that the correlator can not only operate well in other spatial degrees of freedom (e.g., orbital angular momentum) but also be used to establish specific spatial correlations between pseudo-thermal light sources possessing distinct correlation properties. This work opens a new avenue for harnessing uncorrelated classical light in correlation-based optical applications.
Photons emitted by incoherent sources exhibit temporal bunching, a fundamental manifestation of Bose-Einstein statistics first observed by Hanbury Brown and Twiss (HBT). While intensity correlation measurements originated in astronomy and are now central across quantum technologies, biophysics, and spectroscopy, observing temporal bunching in broadband thermal light remains limited by detector temporal resolution. Conventional approaches - such as streak cameras or optical upconversion - introduce severe trade-offs in efficiency, bandwidth, or setup versatility. Here, we propose and demonstrate a third route: pre-detection temporal magnification of the optical field prior to measuring its intensity autocorrelation function in a conventional HBT setup. Using an electro-optic time lens with a temporal magnification of 660, we resolve the temporal intensity autocorrelation of broadband thermal light generated via non-degenerate spontaneous parametric down-conversion with a bandwidth of 250 GHz. This enables direct observation of thermal photon bunching on sub-3.5 picosecond timescales without narrow spectral filtering, establishing pre-detection temporal imaging as a general platform for broadband statistical optics, with applications spanning ultrafast quantum optics, biophysical imaging, and potentially stellar intensity interferometry.
Since Hanbury Brown and Twiss revealed the photon bunching effect of a thermal light source in 1956, almost all studies in correlation optics have been based on light’s intensity fluctuation, regardless of fact that the polarization fluctuation is a basic attribute of natural light. In this work, we uncover the veil of the polarization fluctuation and corresponding photon correlations by proposing a new light source model, termed pseudo-natural light, embodying both intensity and polarization fluctuations. Unexpectedly, the strong antibunching and superbunching effects can be simultaneously realized in such a new source, whose second-order correlation coefficient g ( 2 ) can be continuously modulated across 1. For the symmetric Bernoulli distribution of the polarization fluctuation, particularly, g ( 2 ) can be in principle from 0 to unlimitedly large. In pseudo-natural light, while the bunching effects of both intensity and polarization fluctuations enhance the bunching to superbunching photon correlation, the antibunching correlation of the polarization fluctuation can also be extracted through the procedure of division operation in the experiment. The antibunching effect and the combination with the bunching one will arouse new applications in quantum imaging. As heuristic examples, we carry out high-quality positive or negative ghost imaging, and devise high-efficiency polarization-sensitive and edge-enhanced imaging. This work, therefore, sheds light on the development of multiple and broad correlation functions for natural light.