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International Conference on Transparent Optical Networks

Advances in Quantum imaging

Filip Krajinić, M. M. Ćurčić, B. M. Jelenković

Published Jul 6, 2025• 1 citation
Publisher

Abstract

Quantum states of light are opening new paradigm for imaging, enabling imaging with photons that didn’t interact with the object. Quantum imaging methods discussed here explore quantum correlated photon pairs, generated via spontaneous parametric down conversion (SPDC) in the nonlinear crystal (NLC). We demonstrate generation of highly non-degenerate photon pairs, via SPDC in AGS crystal, with the photon interacting with the object in the mid-infrared (MIR) and the non-interacting in the near-infrared spectral region. Results revealed that the wavelength of the interacting photon can be tuned in a wide spectral range, between 5 μm and 11 μm, covering most of "fingerprint" spectral region. This makes quantum imaging with AGS an alternative to more costly FTIR spectrometers.

DOI
10.1109/icton67126.2025.11125287

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Quantum states of light are opening new paradigm for imaging, enabling imaging with photons that didn’t interact with the object. Quantum imaging methods discussed here explore quantum correlated photon pairs, generated via spontaneous parametric down conversion (SPDC) in the nonlinear crystal (NLC). We demonstrate generation of highly non-degenerate photon pairs, via SPDC in AGS crystal, with the photon interacting with the object in the mid-infrared (MIR) and the non-interacting in the near-infrared spectral region. Results revealed that the wavelength of the interacting photon can be tuned in a wide spectral range, between 5 μm and 11 μm, covering most of "fingerprint" spectral region. This makes quantum imaging with AGS an alternative to more costly FTIR spectrometers.
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Abstract The nonlinear process of spontaneous parametric down-conversion in the silver-gallium-sulfide crystal can generate highly non-degenerate photon pairs in near-infrared and mid-infrared spectral ranges. In this work, we demonstrate and characterize the tunable mid-infrared photon source in silver-gallium-sulfide. By angle tuning the phase matching condition of the nonlinear crystal, we can tune the wavelength of the generated photons in mid-infrared from 5.661 to 10.885 μm (from 1766 to 919 cm −1 ), while the correlated photons in the near-infrared are from 747.1 to 702.6 nm. The phase matching curve and the frequency-angular spectrum of mid-infrared photons were experimentally validated by measuring the properties of near-infrared photons. The brightness of the photon pair source was found to be (29.2± 1.1) MHzmW\frac{\text{MHz}}{\text{mW}}mWMHz​ in the low-gain regime, exceeding the values reported in previous studies using silver-gallium-sulfide crystals. The wide tunability of the photon source in the mid-infrared range is important for hyperspectral imaging and sensing, and it is of significant interest for biomedical, chemical, and environmental applications.
We demonstrate nondegenerate photon pair generation by spontaneous parametric downconversion in a silver gallium sulfide AgGaS2 crystal. By tuning the pump wavelength, we achieve phase matching over a large spectral range. This allows to generate idler photons in the mid-infrared spectral range above a 6 μm wavelength with corresponding signal photons in the visible. Also, we show photon pair generation with broad spectral bandwidth. These results are a valuable step toward the development of quantum imaging and sensing techniques in the mid-infrared.
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Abstract We report the generation of highly non-degenerate spontaneous parametric down conversion (SPDC) in a novel mid-infrared nonlinear crystal BaGa 2 GeS 6 , and provide a direct experimental comparison with the widely used AgGaS 2 crystal. Using a continuous-wave near-infrared (near-IR) pump laser, we generate correlated photon pairs with signal wavelengths in the near-IR ∼815–900 nm and idler wavelengths extending deep into the mid-infrared (mid-IR) up to 22–24 µ m. Wavelength-angular SPDC spectra are measured for both crystals under identical experimental conditions and analyzed using available dispersion data. Our results demonstrate, for the first time, the efficient generation of correlated photon pairs in BaGa 2 GeS 6 via SPDC. A quantitative comparison shows that BaGa 2 GeS 6 exhibits approximately twice the nonlinear conversion efficiency of AgGaS 2 , which is in good agreement with values reported in the literature. In addition, BaGa 2 GeS 6 produces a narrower external SPDC emission cone due to its lower refractive indices, which is advantageous for photon collection and nonlinear interferometric applications. Due to its large effective second-order nonlinearity and broad mid-IR transparency BaGa 2 GeS 6 emerges as a highly promising platform for bright and stable sources of correlated photon pairs. These results establish BaGa 2 GeS 6 as a strong candidate for mid-IR quantum spectroscopy, imaging, and gas-sensing applications.