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Journal of the Optical Society of America B

Wavelength variable generation and detection of photon pairs in visible and mid-infrared regions via spontaneous parametric downconversion

Masaya Arahata, Yu Mukai, Bo Cao, Toshiyuki Tashima, Ryo Okamoto, Shigeki Takeuchi

Published May 5, 2021• 20 citations
Publisher

Abstract

We report an experimental demonstration of wavelength variable generation and detection of photon pairs in the visible and mid-infrared (MIR) regions over a wide spectral range of 2–5 µm via spontaneous parametric downconversion. Despite the recent increase in interest in such a photon-pair source, there have been few detailed evaluations of emitted photons generated via the downconversion process in the low gain regime, due to the lack of suitable single-photon detectors. By changing the angle of the nonlinear crystal, we continuously tune the phase-matching condition and generate photon pairs as signal photons in the wavelength range of 600–965 nm and idler photons in the wavelength range of 1186–4694 nm. We evaluate the generated photon pairs using single and coincidence counts by superconducting nanowire single-photon detectors up to a wavelength of 2 µm and detect the intensity using an InSb detector with a lock-in detection system up to 5 µm. From this analysis, a pair generation rate of 10 5 s − 1 per mW of pump power is experimentally obtained for this wavelength range. This work provides a basis for the realization of applications such as heralded MIR single-photon sources, infrared imaging, and infrared spectroscopy based on quantum technologies in the MIR region.

DOI
10.1364/josab.425550

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We report an experimental demonstration of wavelength variable generation and detection of photon pairs in the visible and mid-infrared (MIR) regions over a wide spectral range of 2–5 µm via spontaneous parametric downconversion. Despite the recent increase in interest in such a photon-pair source, there have been few detailed evaluations of emitted photons generated via the downconversion process in the low gain regime, due to the lack of suitable single-photon detectors. By changing the angle of the nonlinear crystal, we continuously tune the phase-matching condition and generate photon pairs as signal photons in the wavelength range of 600–965 nm and idler photons in the wavelength range of 1186–4694 nm. We evaluate the generated photon pairs using single and coincidence counts by superconducting nanowire single-photon detectors up to a wavelength of 2 µm and detect the intensity using an InSb detector with a lock-in detection system up to 5 µm. From this analysis, a pair generation rate of 10 5 s − 1 per mW of pump power is experimentally obtained for this wavelength range. This work provides a basis for the realization of applications such as heralded MIR single-photon sources, infrared imaging, and infrared spectroscopy based on quantum technologies in the MIR region.
Visible-infrared photon pair sources working in broadband mid-infrared region are useful for applications such as heralded mid-infrared single photon sources. Here, we demonstrate experimentally a wavelength variable visible-infrared photon pair source in the mid-infrared region over a wide spectral range of 2 to 5 μm. By changing the angle of the nonlinear crystal in the source, the observed wavelengths of the signal photons change from 600 to 965 nm, corresponding to the idler wavelengths in 1186-4694 nm.
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.
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.
Quantum measurements using single-photon detectors are opening interesting new perspectives in diverse fields such as remote sensing, quantum cryptography and quantum computing. A particularly demanding class of applications relies on the simultaneous detection of correlated single photons. In the visible and near infrared wavelength ranges suitable single-photon detectors do exist. However, low detector quantum efficiency or excessive noise has hampered their mid-infrared (MIR) counterpart. Fast and highly efficient single-photon detectors are thus highly sought after for MIR applications. Here we pave the way to quantum measurements in the MIR by the demonstration of a room temperature coincidence measurement with non-degenerate twin photons at about 3.1 μm. The experiment is based on the spectral translation of MIR radiation into the visible region, by means of efficient up-converter modules. The up-converted pairs are then detected with low-noise silicon avalanche photodiodes without the need for cryogenic cooling.
Mid-infrared (MIR) spectroscopy serves as a powerful tool for molecular structure identification and chemical composition analysis. However, conventional Fourier-transform infrared spectrometers (FTIR) demonstrate compromised signal-to-noise ratios (SNR) under low-light conditions, which severely limit their performance in high-sensitivity applications. Although MIR superconducting nanowire single-photon detectors (SNSPDs) offer high detection efficiency and low timing jitter, their performance is hindered by background dark counts caused by room-temperature blackbody radiation. In this work, we present a quantum-correlated absorption spectroscopy platform that combines MIR-SNSPDs with entangled photon pairs to overcome these limitations. Leveraging the intrinsic temporal and spectral correlations of the photon pairs, coincidence detection effectively distinguishes signal photons from dominant thermal noise, achieving a remarkable improvement of two orders of magnitude in SNR under ultralow pump power conditions. The system achieves a spectral coverage of 3350-3540 nm with a resolution of 3.7 cm -1 at 3.4 µm, operating at an ultralow illumination photon flux of 4.4 × 10 6 photons/s. Validation experiments using polystyrene and polyethylene samples successfully detected CH 2 vibrational modes, demonstrating the platform’s capability for ultrasensitive biochemical analysis and material characterization. By integrating quantum correlation with MIR-SNSPDs, this work establishes a new paradigm for high-performance MIR spectroscopy in low-light scenarios.
Quantum-enhanced optical technologies operating within the 2- to 2.5-μm spectral region have the potential to revolutionize emerging applications in communications, sensing, and metrology. Currently, sources of entangled photons are available at visible, near-infrared and telecom wavelengths but are strongly underdeveloped at longer wavelengths. Here, using custom-designed lithium niobate crystals for spontaneous parametric down-conversion and tailored superconducting nanowire single-photon detectors, we demonstrate two-photon interference and polarization-entangled photon pairs at 2090 nm. These results open the 2- to 2.5-μm mid-infrared window for the development of optical quantum technologies such as quantum key distribution in next-generation mid-infrared fiber communication systems and future Earth-to-satellite communications.