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arXiv:2412.17633 · Nanophotonics

Ultra‐sensitive heterodyne detection at room temperature in the atmospheric windows

Mohammadreza Saemian, Livia Del Balzo, Djamal Gacemi, Yanko Todorov, Étienne Rodriguez, Olivier Lopez, Benoît Darquié, Lianhe H. Li, Alexander Giles Davies, E. H. Linfield, Angela Vasanelli, Carlo Sirtori

Published Jan 17, 2024• 8 citations
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Abstract

We report room temperature heterodyne detection of a quantum cascade laser beaten with a local oscillator on a unipolar quantum photodetector in two different atmospheric windows, at 4.8 µm and 9 µm. A noise equivalent power of few pW is measured by employing an active stabilization technique in which the local oscillator and the signal are locked in phase. The measured heterodyne noise equivalent power is six orders of magnitude lower than that obtained with direct detection.

DOI
10.1515/nanoph-2023-0787

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AIP Advances•Jul 1, 2019•13 citations
We report room temperature heterodyne detection of a quantum cascade laser beaten with a local oscillator on a unipolar quantum photodetector in two different atmospheric windows, at 4.8 µm and 9 µm. A noise equivalent power of few pW is measured by employing an active stabilization technique in which the local oscillator and the signal are locked in phase. The measured heterodyne noise equivalent power is six orders of magnitude lower than that obtained with direct detection.
Abstract Balanced heterodyne detection (BHD) is a key technology at visible and near‐infrared wavelengths for quantum communication and quantum sensing applications based on coherent read‐out schemes. Extending BHD at mid‐infrared wavelengths (4–11 µm), given the reduced scattering and favourable transparent atmospheric windows, could enable robust earth‐satellite links and few‐photon imaging in high‐noise environments. Currently, quantum applications at these wavelengths are hindered by the lack of high‐sensitivity, room‐temperature photoreceivers; moreover, mid‐infrared single‐photon‐detectors reported to date (superconductors, single‐electron‐transistors, or avalanche‐photodiodes) require cryogenic operation, limiting practicality. Here, a room‐temperature BHD system operating at 4.6 µm‐wavelength with atto‐watt sensitivity level, corresponding to a few tens of photons per second, is demonstrated. This result is obtained by selecting commercially available photodetectors with the highest detectivity and exploiting two heterodyne setups ‐one involving a single quantum‐cascade‐laser (QCL) and an acousto‐optic‐modulator (AOM), and the other one including two QCLs with mutual coherence ensured by a phase‐locked‐loop. Combining a sufficiently high local oscillator (LO) power and the high phase‐coherence between signal and LO is crucial to push the system noise‐equivalent‐power (NEP) to values approaching the shot‐noise‐limit, as confirmed by few‐photons interferometry measurements. This work not only validates viable methods to detect ultra‐low‐intensity signals, but is also potentially scalable to the entire wavelength range already accessible by state‐of‐the‐art mid‐infrared technology.
Abstract Single photon detection is the underpinning technology for quantum communication and quantum sensing applications. At visible and near-infrared wavelengths, single-photon-detectors (SPDs) underwent a significant development in the past two decades, with the commercialization of SPADs and superconducting detectors. At longer wavelengths, in the mid-infrared range (4-11µm), given the reduced scattering and favourable transparent atmospheric windows, there is an interest in developing quantum earth-satellites-links and quantum imaging for noisy environments or large-distance telescopes. Still, SPD-level mid-infrared devices have been rarely reported in the state-of-the-art (superconductors, single-electron-transistors or avalanche-photodiodes) and, crucially, all operating at cryogenic temperatures. Here, we demonstrate a room-temperature detection system operating at 4.6µm-wavelength with a sensitivity-level of atto-watt optical power, corresponding to few tens of mid-infrared photons. This result was obtained by exploiting a pair of commercially available photodetectors within two balanced-heterodyne-detection setups: one involving a quantum-cascade-laser (QCL) and an acousto-optic-modulator (AOM) and the other one including two QCLs with mutual coherence ensured by a phase-lock-loop (PLL). Our work not only validates a viable method to detect ultra-low-intensity signals, but is also potentially scalable to the entire wavelength range already accessible by mature QCL technology, unfolding - for the first time - quantum applications at mid- and long-wave-infrared-radiation.
We report here a sensitivity measurement of an all solid-state heterodyne receiver which uses a twin slot antenna coupled, small superconducting NbN hot electron bolometer as mixer and a semiconductor quantum cascade laser operating at 2.8 THz as local oscillator. We measure a double sideband receiver noise temperature of 3200 K at 2.8 THz and 4.2 K. We find that the optimal LO power is 33 nW measured at HEB and 1.3 /spl mu/W estimated at the QCL, much lower than the output power of the QCL. Such a receiver can be used for high-resolution spectroscopy above 2 THz and is particularly suitable for space-based observatories.
The cross-correlation sensitivity of two identical balanced photodiode heterodyne receivers is characterized. Both the balanced photodiodes receive the same weak signal split up equally, a situation equivalent to an astronomical spatial interferometer. A common local oscillator is also split up equally and its phase difference between both the receivers is stabilized. We show by a semi-classical photon deletion theory that the post-detection laser shot noise contributions on both the receivers must be completely uncorrelated in this case of passing three power splitters. We measured the auto- and cross-correlation outputs as a function of the weak signal power (system noise temperature measurement) and obtained a cross-correlation system noise temperature up to 20 times lower than for the auto-correlation system noise temperature of each receiver separately. This is supported by Allan plot measurements showing cross-correlation standard deviations 30 times lower than in auto-correlation. Careful calibration of the source power shows that the auto-correlation (regular) noise temperature of the single balanced receivers is already very near to the quantum limit as expected, which suggests a cross-correlation system noise temperature below the quantum limit. If validated further, this experimentally clear finding will not only be relevant for astronomical instrumentation but also for other fields, such as telecommunications and medical imaging.
We report on the development of a heterodyne receiver at mid-infrared wavelength for high-resolution spectroscopy applications. The receiver employs a superconducting NbN hot electron bolometer as a mixer and a room temperature distributed feedback quantum cascade laser operating at 10.6 μm (28.2 THz) as a local oscillator. The stabilization of the heterodyne receiver has been achieved using a feedback loop controlling the output power of the laser. Improved Allan variance times as well as a double sideband receiver noise temperature of 5000 K and a noise bandwidth of 2.8 GHz of the receiver system are demonstrated.