Dark Count Research Articles

Mid-infrared characterization of NbTiN superconducting nanowire single-photon detectors on silicon-on-insulator

Superconducting nanowire single-photon detectors are widely used for detecting individual photons across various wavelengths from ultraviolet to near-infrared range. Recently, there has been increasing interest in enhancing their sensitivity to single photons in the mid-infrared spectrum, driven by applications in quantum communication, spectroscopy, and astrophysics. Here, we present our efforts to expand the spectral detection capabilities of U-shaped NbTiN-based superconducting nanowire single-photon detectors, fabricated in a 2-wire configuration on a silicon-on-insulator substrate, into the mid-infrared range. We demonstrate saturated internal detection efficiency extending up to a wavelength of 3.5 μm for a 5 nm thick and 50 nm wide NbTiN nanowire with a dark count rate less than 10 counts per second at 0.9 K and a rapid recovery time of 4.3 ns. The detectors are engineered for integration on waveguides in a silicon-on-insulator platform for compact, multi-channel device applications.

Frequency-locked Si3N4 microring for Doppler frequency shift detection

In this paper, we propose to use a homemade all-fiber Si3N4 microring as the frequency discriminator for Doppler frequency shift detection. The full width at half maximum of the microring is 361.83 MHz, which covers the dynamic range of ± 70 m/s for wind measurement applications. By introducing a time-division multiplexing method, we have achieved the frequency locking of the microring to the central frequency of the laser source, which effectively stabilizes the measurement accuracy against perturbations such as temperature fluctuations. By alternatively upshifting and downshifting the pulses, a dual-frequency lasing scheme has been designed to realize the double-edge technique for frequency shift detection. A commercial single-photon detector with 25% quantum efficiency and approximately 1300 Hz dark count rate is used to detect the backscattered signals, which circumvents the need for bulky and expensive superconducting single-photon detectors. The proposed system is validated through an outdoor wind speed detection experiment using a reference anemometer. The experiment results demonstrate the feasibility of using microring as the frequency discriminator and that the precise frequency locking control is able to improve the measurement accuracy to the state-of-the-art level under the influence of perturbations, which highlights the potential for highly integrated direct detection Doppler wind lidar design.

Ge-on-Si single-photon avalanche diode using a double mesa structure.

We present experimental results of Ge-on-Si single-photon avalanche diodes based on a novel, to our knowledge, double mesa structure. Using this structure, the electric field at the mesa edges is suppressed compared to a traditional single mesa, leading to significant performance improvements. The dark current in linear mode shows a smaller increase for larger reverse voltages, resulting in a reduction by more than 260 times at low temperatures. Operated in the Geiger-mode at 110 K, the dark count rate in the double mesa is 100 times smaller. The devices achieve a dark count rate of 953 kHz, a single-photon detection efficiency of 7.3%, and a record-low jitter of 81 ps at an excess bias of 17.6% and a temperature of 110 K.

Superconducting nanowire single-photon detector enhanced near-infrared II portable confocal microscopy for tissue imaging with indocyanine green.

In this Letter a novel, to our knowledge, approach for near-infrared (NIR) fluorescence portable confocal microscopy is introduced, aiming to enhance fluorescence imaging of biological samples in the NIR-II window. By integrating a superconducting nanowire single-photon detector (SNSPD) into a confocal microscopy, we have significantly leveraged the detection efficiency of the NIR-II fluorescence signal from indocyanine green (ICG), an FDA-approved dye known for its NIR-II fluorescence capabilities. The SNSPD, characterized by its extremely low dark count rate and optimized NIR system detection efficiency, enables the excitation of ICG with 1 mW and the capture of low-light fluorescence signals from deep regions (up to 512 µm). Consequently, our technique was able to produce high-resolution images of bio samples with a superior signal-to-noise ratio, making a substantial advancement in the field of fluorescence microscopy and offering a promising opportunity for future clinical study.

Ultra-Low Dark Count Rate SPAD Fully Integrated in a 180 nm High-Voltage CMOS Process

Ultra-Low Dark Count Rate SPAD Fully Integrated in a 180 nm High-Voltage CMOS Process

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When operating in space, on-board Silicon Geiger-Mode Avalanche Photodiodes (GM-APDs) are exposed to radiation damage that result in an increase in dark count rates. Thermal annealing has been found to mitigate the damage, although prior studies have largely focused on annealing following a single session of proton irradiation. This work reports that thermal annealing can be performed simply with the built-in thermo-electric coolers of the GM-APDs. Annealing was also done in 10 min intervals for a clearer view of the recovery curve. Mitigation of damage from repeated γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} radiation was observed from the: (1) halving of the increase in dark count rates on average and (2) outperformance of room temperature annealing (25∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$25\\,^{\\circ }$$\\end{document}C) by 33%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document}. Additionally, we show that heavy doses of γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma $$\\end{document} radiation (21 krad) have a probability of causing Random Telegraph Signals in GM-APDs that can be suppressed by lowering the operating temperature.

Amplitude and time response characterization of avalanche signals in InGaAs single-photon avalanche diode

Photon and dark avalanche signals of InGaAs single-photon avalanche diodes (SPAD) are detected and counted indiscriminately, while their specific characteristics are not well understood, which hinders further performance optimization of InGaAs SPAD. Here, we investigate back-incidence InGaAs SPAD operating at room temperature by designing a dual-threshold discriminator and tuning the threshold voltage. The photon count rate and dark count rates (DCR) exhibit different abrupt-voltage variations with the threshold voltage, and the amplitude distribution of dark avalanche signals is more concentrated and slightly larger than that of photon avalanche signals. The smaller photon avalanche signals have a faster time response. It can be inferred that the above characteristics are related to the photon absorption position and carrier transport, depending on physical structure and operating mode, and dark counts are mainly caused by holes drifting from N-type material. We use a dual-threshold discriminator to reduce the time jitter and DCR caused by thermally excited carriers. The experimental results are in good agreement with theoretical analysis, indicating that the insertion of an i-InP layer or the use of a front-incidence technique can further optimize the overall performance and enable InGaAs SPAD with high performance operation at room temperature.

Parametric Research on the Deep-Junction Silicon SPADs for Wide Spectral Response and Low Dark Count Noise

Parametric Research on the Deep-Junction Silicon SPADs for Wide Spectral Response and Low Dark Count Noise

Feasibility study of YSO/SiPM based detectors for virtual monochromatic image synthesis.

The development of photon-counting CT systems has focused on semiconductor detectors like cadmium zinc telluride (CZT) and cadmium telluride (CdTe). However, these detectors face high costs and charge-sharing issues, distorting the energy spectrum. Indirect detection using Yttrium Orthosilicate (YSO) scintillators with silicon photomultiplier (SiPM) offers a cost-effective alternative with high detection efficiency, low dark count rate, and high sensor gain. This work aims to demonstrate the feasibility of the YSO/SiPM detector (DexScanner L103) based on the Multi-Voltage Threshold (MVT) sampling method as a photon-counting CT detector by evaluating the synthesis error of virtual monochromatic images. In this study, we developed a proof-of-concept benchtop photon-counting CT system, and employed a direct method for empirical virtual monochromatic image synthesis (EVMIS) by polynomial fitting under the principle of least square deviation without X-ray spectral information. The accuracy of the empirical energy calibration techniques was evaluated by comparing the reconstructed and actual attenuation coefficients of calibration and test materials using mean relative error (MRE) and mean square error (MSE). In dual-material imaging experiments, the overall average synthesis error for three monoenergetic images of distinct materials is 2.53% ±2.43%. Similarly, in K-edge imaging experiments encompassing four materials, the overall average synthesis error for three monoenergetic images is 4.04% ±2.63%. In rat biological soft-tissue imaging experiments, we further predicted the densities of various rat tissues as follows: bone density is 1.41±0.07 g/cm3, adipose tissue density is 0.91±0.06 g/cm3, heart tissue density is 1.09±0.04 g/cm3, and lung tissue density is 0.32±0.07 g/cm3. Those results showed that the reconstructed virtual monochromatic images had good conformance for each material. This study indicates the SiPM-based photon-counting detector could be used for monochromatic image synthesis and is a promising method for developing spectral computed tomography systems.

Characterization of neutron-irradiated SiPMs down to liquid nitrogen temperature

Photodetectors used in future high-energy physics experiments will need to keep sufficient performance during a few years of data-taking despite radiation load, which, for example, in the planned upgrade of the Ring Imaging Cherenkov detectors in Large Hadron Collider beauty (LHCb) experiment is estimated at about 1013\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{13}$$\\end{document} 1-MeV neutron equivalent per cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document} (neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document}). Silicon photomultipliers (SiPMs) are considered as candidates for photodetectors for this application. However, their sensitivity to neutron irradiation may seriously compromise their operation, with the increase in dark count rates being the primary limitation after the irradiation. 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In total, 5 SiPMs were irradiated at the Jožef Stefan Institute TRIGA nuclear reactor with different fluences from 109\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{9}$$\\end{document} neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document} up to 1013\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{13}$$\\end{document} neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document}. The SiPMs were also annealed at high temperatures and re-characterized after the annealing. For the SiPM characterization in all the cases, current–voltage (I-V curve) measurements, dark count rate measurements, and waveform analysis, including single photon time resolution, were carried out at different controlled temperature steps from room temperature down to the liquid nitrogen temperature. While cooling to − 20∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C was enough for the SiPM irradiated at 109\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{9}$$\\end{document} neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document} to recover the ability to resolve single photons, by 1013\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{13}$$\\end{document} neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document}, cooling to liquid nitrogen temperature was necessary. With sufficient cooling, the measured single photon time resolution was around 90 ps FWHM for all irradiation levels.

Quantum jump photodetector for narrowband photon counting with a single atom

Using a single neutral Rb87 atom held in an optical trap, and “quantum jump” detection of single-photon-initiated state changes, we demonstrate a single-photon quantum jump photodetector (QJPD) with intrinsically narrow bandwidth and strong rejection of out-of-band photons, of interest for detecting weak optical signals in the presence of a strong broadband background. By analyzing fluorescence photon count distributions for the bright and dark states with and without excitation, we measure quantum efficiency of 2.9(2)×10−3, a record for single-pass quantum jump production, and signal-photon-unprovoked “dark jump” rate—analogous to the dark count rate of other detectors —of 3(10)×10−3jumps/s during passive accumulation plus 4.0(4)×10−3 jumps per readout, orders of magnitude below those of traditional single-photon detectors. Available methods can substantially improve QJPD quantum efficiency, dark jump rate, bandwidth, and tunability. Published by the American Physical Society 2024

Deep Mouse Brain Two-Photon Near-Infrared Fluorescence Imaging Using a Superconducting Nanowire Single-Photon Detector Array.

Two-photon microscopy (2PM) has become an important tool in biology to study the structure and function of intact tissues in vivo. However, adult mammalian tissues such as the mouse brain are highly scattering, thereby putting fundamental limits on the achievable imaging depth, which typically reside at around 600-800 μm. In principle, shifting both the excitation as well as (fluorescence) emission light to the shortwave near-infrared (SWIR, 1000-1700 nm) region promises substantially deeper imaging in 2PM, yet this shift has proven challenging in the past due to the limited availability of detectors and probes in this wavelength region. To overcome these limitations and fully capitalize on the SWIR region, in this work, we introduce a novel array of superconducting nanowire single-photon detectors (SNSPDs) and associated custom detection electronics for use in near-infrared 2PM. The SNSPD array exhibits high efficiency and dynamic range as well as low dark-count rates over a wide wavelength range. Additionally, the electronics and software permit a seamless integration into typical 2PM systems. Together with an organic fluorescent dye emitting at 1105 nm, we report imaging depth of >1.1 mm in the in vivo mouse brain, limited mostly by available labeling density and laser properties. Our work establishes a promising, and ultimately scalable, new detector technology for SWIR 2PM that facilitates deep tissue biological imaging.

A 48×2 CMOS SPAD Sensor With Regulated Dark Count

A 48×2 CMOS SPAD Sensor With Regulated Dark Count

Silicon photomultipliers for future HEP experiments

For the particle identification systems of the future high-energy physics detectors, single-photon sensors with sub-mm granularity, high sensitivity, and mitigation strategy for operation in the neutron-irradiated areas are needed. Silicon photomultipliers are considered a baseline technology because of their high photon detection efficiency, good timing resolution, and low operating voltage compared to those of vacuum-based photo sensors. After neutron irradiation, the dark counts increase dramatically and distort the signal baseline, making the single photons indistinguishable. Although the DCR of different unirradiated SiPMs varies, the devices show very similar rates when irradiated to high doses. In this work, we investigated the performance parameters of FBK NUV-HD-RH UHD-DE 1 mm2 devices and determined the working temperature. We show that the maximum operation temperature for samples irradiated with a fluence of 1012 neq/cm2 is around -100°C.

Robust Pixel Design Methodologies for a Vertical Avalanche Photodiode (VAPD)-Based CMOS Image Sensor.

We present robust pixel design methodologies for a vertical avalanche photodiode-based CMOS image sensor, taking account of three critical practical factors: (i) "guard-ring-free" pixel isolation layout, (ii) device characteristics "insensitive" to applied voltage and temperature, and (iii) stable operation subject to intense light exposure. The "guard-ring-free" pixel design is established by resolving the tradeoff relationship between electric field concentration and pixel isolation. The effectiveness of the optimization strategy is validated both by simulation and experiment. To realize insensitivity to voltage and temperature variations, a global feedback resistor is shown to effectively suppress variations in device characteristics such as photon detection efficiency and dark count rate. An in-pixel overflow transistor is also introduced to enhance the resistance to strong illumination. The robustness of the fabricated VAPD-CIS is verified by characterization of 122 different chips and through a high-temperature and intense-light-illumination operation test with 5 chips, conducted at 125 °C for 1000 h subject to 940 nm light exposure equivalent to 10 kLux.

Dark counts in optical superconducting transition-edge sensors for rare-event searches

Dark counts in optical superconducting transition-edge sensors for rare-event searches

Measurement of photo- and radio-luminescence of thin ThF[formula omitted] films

We conducted measurements on the photo- and radio-luminescence of thin ThF4 films in both the UV and visible ranges. In the UV range, we found that both luminescences are at a similar level as the internal dark counting noise of the photo-multiplier-tube (PMT). Our results suggest that thin ThF4 crystals could be used as a target for the search for 229mTh and as a medium for the future nuclear clock. The measurements indicate that using a small and thin ThF4 film can reduce background noise while maintaining the signal at the same level, achieved by increasing the 229Th enrichment. Our developed apparatus is now ready for direct measurements of 229mTh excitation and decay in ThF4.

Avalanche Terahertz Photon Detection in a Rydberg Tweezer Array.

We propose a protocol for the amplified detection of low-intensity terahertz radiation using Rydberg tweezer arrays. The protocol offers single photon sensitivity together with a low dark count rate. It is split into two phases: during a sensing phase, it harnesses strong terahertz-range transitions between highly excited Rydberg states to capture individual terahertz photons. During an amplification phase it exploits the Rydberg facilitation mechanism which converts a single terahertz photon into a substantial signal of Rydberg excitations. We discuss a concrete realization based on realistic atomic interaction parameters, develop a comprehensive theoretical model that incorporates the motion of trapped atoms and study the many-body dynamics using tensor network methods.

Feasibility study of photon-counting CT for material identification based on YSO/SiPM detector: A proof of concept.

Current photon-counting computed tomography (CT) systems utilize semiconductor detectors, such as cadmium telluride (CdTe), cadmium zinc telluride (CZT), and silicon (Si), which convert x-ray photons directly into charge pulses. An alternative approach is indirect detection, which involves Yttrium Orthosilicate (YSO) scintillators coupled with silicon photomultipliers (SiPMs). This presents an attractive and cost-effective option due to its low cost, high detection efficiency, low dark count rate, and high sensor gain. This study aims to establish a comprehensive quantitative imaging framework for three-energy-bin proof-of-concept photon-counting CT based on YSO/SiPM detectors developed in our group using multi-voltage threshold (MVT) digitizers and assess the feasibility of this spectral CT for material identification. We developed a proof-of-concept YSO/SiPM-based benchtop spectral CT system and established a pipeline for three-energy-bin photon-counting CT projection-domain processing. The empirical A-table method was employed for basis material decomposition, and the quantitative imaging performance of the spectral CT system was assessed. This evaluation included the synthesis errors of virtual monoenergetic images, electron density images, effective atomic number images, and linear attenuation coefficient curves. The validity of employing A-table methods for material identification in three-energy-bin spectral CT was confirmed through both simulations and experimental studies. In both noise-free and noisy simulations, the thickness estimation experiments and quantitative imaging results demonstrated high accuracy. In the thickness estimation experiment using the practical spectral CT system, the mean absolute error for the estimated thickness of the decomposed Al basis material was 0.014±0.010mm, with a mean relative error of 0.66%±0.42%. Similarly, for the decomposed polymethyl methacrylate (PMMA) basis material, the mean absolute error in thickness estimation was 0.064±0.058mm, with a mean relative error of 0.70%±0.38%. Additionally, employing the equivalent thickness of the basis material allowed for accurate synthesis of 70keV virtual monoenergetic images (relative error 1.85%±1.26%), electron density (relative error 1.81%±0.97%), and effective atomic number (relative error 2.64%±1.26%) of the tested materials. In addition, the average synthesis error of the linear attenuation coefficient curves in the energy range from 40 to 150keV was 1.89%±1.07%. Both simulation and experimental results demonstrate the accurate generation of 70keV virtual monoenergetic images, electron density, and effective atomic number images using the A-table method. Quantitative imaging results indicate that the YSO/SiPM-based photon-counting detector is capable of accurately reconstructing virtual monoenergetic images, electron density images, effective atomic number images, and linear attenuation coefficient curves, thereby achieving precise material identification.

Using superconducting single photon detector to improve the coupling efficiency of multimode fibers in the telescope ranging system

The receiving system adopts the coupling manner of space beam and the multimode fiber among some space target laser ranging system. The fiber coupling efficiency can affect the number of echo photons and ranging accuracy, especially in lunar laser ranging, high orbit satellite laser ranging and space debris tracking. This article proposes a method utilizing the telescope pointing technique and a four-pixel superconducting nanowire single photon detector (SNSPDs) to measure coupling efficiency of multimode fiber. SNSPDs has the excellent performance with high detection efficiency, low dark count rate, and low recovery time. In the experiment, SNSPDs receives the changing signals caused by adjusting the offset angle of the telescope. The root mean square of deviation between measured results and theoretical calculations is 4.48%. The method is based on existing laser ranging systems and is suitable for scientific engineering verification of optical fibers already installed in the system and monitoring of system status.