KEYWORDS: Signal to noise ratio, Single mode fibers, Light sources, Astronomical imaging, Beam splitters, Light sources and illumination, Interferometry
Dark-field techniques are successfully used in microscopy for increasing the contrast of almost transparent objects, and for edge detection by removing image components with low spatial frequencies. A removal of image components with little interesting information but high intensity yields a higher signal-to-noise ratio for the image components of interest. Here, we present a technique to enhance the signal-to-noise ratio of an image signature contained in a spatial asymmetry. While being an interferometric technique based on image inversion, it will work with incoherent light sources, and thus be applicable in many practical imaging scenarios. We experimentally demonstrate an increase of the signal-to-noise ratio in asymmetry detection by an order of magnitude in a proof-of-principle experiment.
Conventional optical ranging techniques require timing modulated light sources to provide for the time-of-flight information, which may allow for detection, jamming or decoy by a third-party with information to the modulation pattern. Quantum ranging techniques, or quantum lidar, use spontaneous parametric down converted light sources to provide the timing correlation, where entanglement is not necessarily exploited in the simplementation, and is complex and expensive. Here we propose the use of stationary broadband light generated from a laser diode operating below threshold to provide the timing correlation, as extracted from thermal photon bunching.
Characterizing the temporal response function of single-photon detectors (SPDs) is essential for quantum communication protocols and time-resolved measurements. Typically, this characterization is obtained from the arrival time statistics of photons from a pulsed laser. In this work, we present an alternative approach using time-correlated photon pairs generated in spontaneous parametric down-conversion (SPDC). We demonstrate a continuous wavelength-tunability from 526 nm to 661 nm for one photon of the pair, and 1050 nm to 1760 nm for the other photon a range comparable to existing pulsed-laser systems. With this source, we characterized single-photon avalanche detectors sensitive to the two distinct wavelength bands, one based on Silicon, the other based on Indium Gallium Arsenide.
Classical sensing techniques such as range finding and clock synchronization use timing modulated light sources to provide the timing correlations needed for their implementation. Corresponding quantum schemes utilise spontaneous parametric down converted light sources to provide the timing correlations without the need for timing modulation, although entangled states are too fragile to be fully exploited presently. Here we demonstrate the use of thermal light as an alternative source for timing correlations, via the photon bunching generated from a laser operating below threshold, and showcase its practical viability by successful range finding measurements.
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