Dark Count Research Articles

Ultra-sensitive UV solar-blind optical wireless communications with an SiPM.

In this Letter, an SiPM with a dedicated cooling system suitable for receiving ultra-low-power solar-blind wavelengths is reported. This is designed to decrease the temperature of the detector from 21°C to -10°C, and the corresponding dark count rate (DCR) is reduced by approximately 10 dB. A 275 nm optical wireless communication (OWC) system is established using on-off-keying (OOK) modulation. Transmission rates ranging from 100 kbit/s to 2 Mbit/s are demonstrated with this cooled SiPM. The received power is as low as 30 pW (corresponding to 41.5 photons per bit) at a data rate of 1 Mbit/s and a bit error rate of 2.4 × 10-3.

Characterization of Hamamatsu S13161-3050AE-08 SiPM (8 × 8) array at different temperatures with CAEN DT5202

Silicon PhotoMultipliers, SiPMs, constitute the enabling technology for a diverse and rapidly growing range of applications: medical imaging, experimental physics, and commercial applications are only a few examples. In this work, a characterization protocol for SiPM qualification has been applied to Hamamatsu S13161-3050AE-08 SiPM (8 × 8) array in the (−40 ÷ ＋30) °C temperature range. The protocol foresees to measure several parameters: breakdown voltage, quenching resistance, gain, dark count rate and probability of cross-talk. Methods to extract them and their dependence on temperature at fixed overvoltage are shown and the results are discussed.

Phase encoded quantum key distribution up to 380 km in standard telecom grade fiber enabled by baseline error optimization

Phase encoding in quantum key distribution (QKD) enables long-distance information-theoretic secure communication in optical fibers. We present a novel theoretical model characterizing errors from various sources in practical phase encoding-based QKD systems, namely the laser linewidth, detector dark counts, and channel dispersion. This model provides optimized optical pulse parameters and less distortion in pulses, which eliminates system imperfections and leads to a reduced quantum bit error rate (QBER) for practical QKD scenario. This analysis is applicable to various fiber-based phase and time encoding protocols. In particular, we implement this to a differential phase shift (DPS) QKD scheme operating at a 2.5 GHz clock, which produces a secure key rate of 193 bits/s at a fiber length of 265 km and an unprecedented QBER < 1% up to 225 km length with standard telecom components. We show that by adjusting the quantum efficiency and dark count rates of detectors, proposed system can establish secure keys up to 380 km distance using standard telecom grade fiber with a QBER of 1.48%. Moreover, the system is compatible with existing optical fiber networks and capable of establishing a secure key exchange between two cities 432 km apart using ultra-low-loss (ULL) specialty fiber.

Design and simulation of a near-infrared enhanced Si-based SPAD for an automotive LiDAR.

A near-infrared (NIR)-enhanced single-photon avalanche diode (SPAD) with a retrograded NM/XP junction for an automotive LiDAR was designed based on CSMC 0.18µm BCD technology. A 3µm depth NM/XP junction embedded in a lightly doped deep p-well (DP) improves the absorption efficiency in the NIR regime; the photo-generated electrons generated in the depletion region are efficiently collected into the central multiplication region by a drift process, and then the impact ionization is triggered by the strong field, resulting in a high photon detection efficiency (PDE). Additionally, the deep NM/XP junction and the buried layer effectively isolate the dark noise originating from the interface and the substrate. The SPAD was initially simulated by numerical calculation, and then was evaluated with active quench/reset electronics in a circuit simulator. The results revealed that the SPAD with an active area of 314µm 2 achieves a PDE of 16.2% at 905nm and a dark count rate (DCR) of 1.46H z/µm 2, with an excess bias of 5V at room temperature. The designed SPAD is well suited for the low-cost, miniaturized automotive LiDAR.

Performance of the most recent Microchannel-Plate PMTs for the PANDA DIRC detectors at FAIR

In the PANDA experiment at the FAIR facility at GSI two DIRC (Detection of Internally Reflected Cherenkov light) detectors will be used for π/K separation up to 4GeV/c. Due to their location in a high magnetic field and other stringent requirements like high detection efficiency, low dark count rate, radiation hardness, long lifetime and good timing, MCP-PMTs (microchannel-plate photomultiplier) were the best choice of photon sensors for the DIRC detectors in the PANDA experiment. This paper will present the performance of some of the latest 2 × 2inch 2 MCP-PMTs from Photek and Photonis, including the first mass production tubes for the PANDA Barrel DIRC from Photonis. Performance parameters like the collection efficiency (CE), quantum efficiency (QE), and gain homogeneity were determined. The effect of magnetic fields on some properties like gain and charge cloud width was investigated as well. Apart from that the spatial distribution of many internal parameters like time resolution, dark count rate, afterpulse ratio, charge sharing crosstalk and recoil electrons were measured simultaneously with a multihit capable DAQ system. The latest generation of Photonis MCP-PMTs shows a unexpected ”escalation” effect where the MCP-PMT itself produces photons.

In-situ measurement techniques for space plasmas based on floating-mode avalanche photodiode and electrostatic energy-per-charge analyzer

New instrumental developments based on a floating-mode avalanche photodiode (APD) combined with an electrostatic energy-per-charge analyzer were conducted for comprehensive and accurate plasma measurements in wide energy ranges in future space plasma explorations. The advantages of APD, namely, rough energy analysis capability, low dark count, compact dimension, and lightweight, are promising as an advanced in-situ measurement technique. We conducted several types of electron/ion beamline experiments under different floating voltage conditions in order to investigate the properties of particle detections and energy analyses using the floating/normal-mode APD combined with/without the electrostatic energy-per-charge analyzer. The electron/ion post-acceleration associated with the operation of APD in floating mode reduces the lowermost energies detectable by APD. Applying a high voltage of ∼ ±5 kV to electrostatically float APD in the combination with an electrostatic analyzer, we can attain wide energy coverages (∼ eV – 100's of keV for electrons, ∼ 5 keV/q – 100's of keV/q for ions) with proper energy resolutions, noise reduction due to double energy discrimination, and ion mass discrimination capability particularly to distinguish energetic He2+ components of solar wind origin. This technique would also be useful to distinguish the terrestrial-origin O+ from H+ in energies of > a few tens of keV if the ions outflowing from the Earth’s upper atmosphere significantly affect the plasma population after some energization processes in the magnetosphere. When these advanced in-situ measurement techniques are employed in future exploration missions, wide-energy/angular distributions of both electrons and ions in space could be captured simultaneously by a single sensor head with triple-dome structure on spin-stabilized satellite.

Photo-Trap: A low-cost and low-noise large-area SiPM-based pixel

The small sensitive area of commercial silicon photomultipliers (SiPMs) is often the main limitation for their use in experiments and applications that require large detection areas. Since capacitance, dark count rate and cost increase with the SiPM size, they are rarely found in sizes larger than 6 × 6 mm2. Photo-Trap combines a wavelength-shifter plastic, a dichroic filter and a standard commercial SiPM to build pixels of a few cm2. With this approach it can collect light over an area that can be ∼10–100 times larger than the area of a commercial SiPM, while keeping the noise, single-photoelectron resolution, power consumption and likely the cost of a single small SiPM. We developed four different proof-of concept pixels sensitive in the near UV band, the largest one being of 40 × 40 mm2. We characterized them through laboratory measurements and Geant4 simulations. The optical gain we measured with the prototypes went from ∼5 to ∼15, while the single-photon time resolution was of ∼3–5 ns FWHM. With the achieved performance Photo-Trap could be a competitive low-cost alternative for applications that require photosensors with large collection areas and low noise, such as dark matter experiments and optical wireless communication.

Large Area Picosecond Photodetector for the Upgrade II of the LHCb RICH

The Large Area Picosecond Photodetector (LAPPD) is a new generation microchannel plate (MCP) photodetector that is currently capturing the attention of detector physicists thanks to its excellent timing resolution, high gain and low dark count rate. It consists of a photocathode that responds to a single photon by producing a photoelectron that enters a pair of microchannel plates, where it is multiplied to a million electrons in a fast-rising pulse that is easily detected. The speed of this process provides the time resolution essential for high intensity environments such as the high luminosity Large Hadron Collider (LHC) at the CERN laboratory. The LAPPD has a large sensitive area, 200 × 200 mm 2, which reduces the number of sensors that are needed. The increased particle collision rate in the future LHC-HL phase represents a great challenge for the Ring Imaging Cherenkov (RICH) photodetectors in the LHCb experiment. The LHCb collaboration is working for the Upgrade II that will take place during the Long Shutdown 4 of the LHC (>2032). The LAPPD produced and commercialised by INCOM (US) represents one of the possible alternatives for the future RICH photodetectors, thanks to its good time resolution, low dark noise rate and high gain. The LHCb Edinburgh group is involved in the Upgrade II R&D programme, testing and characterising an LAPPD in the laboratory of the University. The LAPPD technology, the current Edinburgh setup and performance from first tests of the photodetector will be presented.

Effective suppression of dark counts in superconducting microstructures with grid of pinholes in a magnetic field

In a magnetic field, vortices significantly contribute to the dark counts of single-photon detectors made of superconducting wires, and they are also limiting the critical current of such devices. To address this issue, we prepared superconducting microwires with a pinhole grid from WSi thin films and report on corresponding critical-current and count-rate measurements in an external magnetic field B. When compared to corresponding devices without pinholes, the critical current only weakly depends on the magnetic field at B < 16 mT and it is even larger already at B > 10 mT. Moreover, dark counts are not only suppressed in zero field, but particularly in magnetic fields B < 16 mT, while photon counts are virtually field insensitive in the same range of the magnetic field.

Investigation of dark count rate in NbRe microstrips for single photon detection

Superconducting microstrip single photon detectors (SMSPDs) received great interest since they are expected to combine the excellent performance of superconducting nanostrip single photon detectors with the possibility to cover large active areas using low-cost fabrication techniques. In this work, we fabricated SMSPDs based on NbRe to investigate the role of vortices in the dark counts events in this innovative material and in devices with micrometer size. We realized devices with different layouts, namely single microstrips and pairs of parallel microstrips. The energy barriers related to the motion of single vortices or vortex–antivortex pairs, responsible of detection events, have been determined and compared with the ones of similar devices based on different materials, such as MoSi, WSi and NbN. The analysis confirms the high potential of NbRe for the realization of superconducting single photon detectors with large areas.

Mobile superconducting strip photon detection system with efficiency over 70% at a 1550 nm wavelength.

We developed a mobile superconducting strip photon detector (SSPD) system operated in a liquid-helium Dewar. By adopting highly disordered NbTiN thin films, we successfully enhanced the detection performance of superconducting strips at higher operation temperatures and realized SSPDs with nearly saturated detection efficiency at 4.2 K. Then we customized a compact liquid-helium Dewar and a battery-based electronic module to minimize the SSPD system. A mobile SSPD system was integrated, which showed a system detection efficiency of 72% for a 1550 nm wavelength with a dark count rate of 200 cps and a timing jitter of 67.2 ps. The system has a weight of 40 kg and a power consumption of 500 mW, which can work continuously for 20 hours. The metrics can be further optimized in accordance with the various practical application platforms, such as aircraft, drones, etc.

Research on 3D image reconstruction of sparse power lines by array GM-APD lidar

Power lines and other tiny obstacles in the air are deadly hazards to safe aircraft flight. However, existing detection methods have difficulty sensing power lines’ weak radiation signals submerged in noise, making power lines detection an international research hotspot. To solve this problem, this paper proposes the use of array Geiger-mode avalanche photodiode (GM-APD) light detection and ranging (lidar) with single photon detection sensitivity to achieve remote three-dimensional (3D) imaging detection of power lines (GM-PLTR). We focus on solving the problem of noise filtering for sparse power lines under low Signal-to-noise ratio (SNR) conditions and completing 3D image reconstruction. Firstly, we propose a method based on adaptive thresholding and waveform density discrimination combined with spatial dependency to remove the pixel-wise noise, including environmental light, noise echoes from neighboring pixels, and dark count noise. Then we obtain the high SNR depth image of the targets. Secondly, we use an improved DBSCAN algorithm to separate the power lines from the background noise in the depth image to improve the reconstruction effect. Finally, we use a one-directional template matching method to fill in the missing shapes of the power lines. Experimental results show that the algorithm improves the SNR of the power lines echo signal by an average of 2.3 times and achieves sparse power lines imaging detection at 340.95 m. Moreover, the Hough transform confirms the possibility of high-precision detection of power lines, significantly reducing the difficulty of detecting small targets. Finally, it will help unmanned aerial vehicles (UAVs) complete the inspection of power lines.

(Invited) New Approaches for Frequency-Resolving Single Photon Detection Based on Nanoscale Systems

Single photon detectors play a key role across a number of basic science and technology applications. While progress has been made in improving performance, single photon detectors that can maintain high performance while also resolving the photon frequency are still lacking. In this presentation, I will discuss how a photodetector architecture composed of nanoscale elements that cooperatively interact with the photon field can simultaneously achieve high efficiency, low jitter, low dark count rate, and high frequency resolution. A potential physical realization of such an architecture utilizing carbon nanotubes will be presented.

Enhancing SNSPDs detection efficiency via suspended SiO2 membrane

Superconducting nanowire single-photon detectors (SNSPDs) with high detection efficiency have played significant role in numerous applications for photon detection from visible light to mid-infrared band. However, it is still a challenge to easily promote the sensitivity of SNSPD without compromising its other performance. We report a method to improve the detection sensitivity of devices via suspended SiO2 membrane, and the intrinsic detection efficiency is significantly enhanced from 78% to 100% for a 1550 nm wavelength. The electro-thermal simulation and hotspot relaxation time measurement indicate that a suspended SiO2 membrane can significantly decrease the cooling efficiency between the hotspot and the substrate, and the relaxation time is enlarged twice than before. Meanwhile, we note that the proposed method does not affect other properties of devices, such as dark count rate, detection speed, and timing jitter. Because the thermal dissipation process can be controlled continuously (by varying the size of the suspended area), the proposed method may also help to obtain a deeper understanding of the thermal diffusion and detection process of SNSPDs.

Study of radiation effects on SiPM for an optical readout system for the EIC dual-radiator RICH

Silicon photomultipliers (SiPM) are the potential candidate photodetector technology selected for the dual-radiator Ring-Imaging Cherenkov (dRICH) detector of the future Electron-Ion Collider (EIC). SiPM are inexpensive devices, with high detection efficiency and insensitive to the high magnetic field experienced at the expected location of the sensors in the experiment. On the other hand, SiPM are susceptible to radiation damage. The integrated radiation level at the location of the sensors in the experiment is expected to be moderate, nonetheless it should be tested whether the capabilities for single photon-counting can be maintained to ensure the optimal dRICH detector performance across the years keeping the dark count rates under control as well. In this paper, the current status of the research studies performed for the EIC dRICH application and the first results on a sample of commercial and prototype SiPM sensors are presented.

Study of Proton-Induced Defects in 40-nm CMOS SPADs

Defects induced by 62 MeV protons in SPADs are studied. A study of the Dark Count Rate (DCR) variation after irradiations for different biasing conditions underlines the predominance of field enhancement effects such as Poole-Frenkel effect and phonon-assisted-tunneling over band-to-band tunneling. Activation energy measurements below mid-gap value confirm the important contribution of these field effects. However, unexpected behaviors in these energies are seen: very low activation energies are extracted for SPADs with a DCR induced around 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> counts per second. We attribute them to the contribution of different groups of defects, with different energy level distribution. This analysis is completed with an annealing study between 100 °C and 300 °C. Results for high DCR SPADs correlate well with the presence of defect clusters. Moreover, histogram of the annealing temperature at which the DCR starts to drop displays two peaks at 170 °C and 250 °C. The first one is attributed to phosphorus vacancies and complex cluster of defects with an energy distribution inside the Si bandgap centered above mid-gap. The second one is attributed to clusters of divacancies that also anneal at temperatures around 250 °C.

Integration of thermo-electric coolers into the CMS MTD SiPM arrays for operation under high neutron fluence

Abstract The barrel section of the novel MIP Timing Detector (MTD) will be constructed as part of the upgrade of the CMS experiment to provide a time resolution for single charged tracks in the range of 30–60 ps using LYSO:Ce crystal arrays read out with Silicon Photomultipliers (SiPMs). A major challenge for the operation of such a detector is the extremely high radiation level, of about 2 × 1014 1 MeV(Si) Eqv. n/cm2, that will be integrated over a decade of operation of the High Luminosity Large Hadron Collider (HL-LHC). Silicon Photomultipliers exposed to this level of radiation have shown a strong increase in dark count rate and radiation damage effects that also impact their gain and photon detection efficiency. For this reason during operations the whole detector is cooled down to about -35°C. In this paper we illustrate an innovative and cost-effective solution to mitigate the impact of radiation damage on the timing performance of the detector, by integrating small thermo-electric coolers (TECs) on the back of the SiPM package. This additional feature, fully integrated as part of the SiPM array, enables a further decrease in operating temperature down to about -45°C. This leads to a reduction by a factor of about two in the dark count rate without requiring additional power budget, since the power required by the TEC is almost entirely offset by a decrease in the power required for the SiPM operation due to leakage current. In addition, the operation of the TECs with reversed polarity during technical stops of the accelerator can raise the temperature of the SiPMs up to 60°C (about 50°C higher than the rest of the detector), thus accelerating the annealing of radiation damage effects and partly recovering the SiPM performance.

PeakOTron: A Python module for fitting charge spectra of Silicon Photomultipliers

A Python program has been developed which fits a published detector-response model to SiPM charge spectra to characterise SiPMs. Spectra for SiPMs illuminated by low intensity pulsed light with Poisson-distributed number of photons and a time spread of order nanoseconds or less, and spectra without illumination can be analysed. The entire spectra, including the intervals in-between the photoelectron peaks, are fitted, which allows determining, in addition to the mean number of detected photons, gain, gain spread, prompt cross-talk, pedestal, and electronics noise, the dark-count rate as well as the probability and time constant of after-pulses. The starting values of the fit parameters are extracted from the charge spectra.The program performance has been evaluated using simulated charge spectra with the different SiPM parameters varied in a wide range. By analysing 100 simulated spectra for every parameter set, the biases and statistical uncertainties of the individual parameters have been determined. It is found that the parameters are precisely determined and that the entire spectra are well described, in most cases with a χ2/NDF close to 1. In addition, measured spectra for two types of SiPMs for a wide range of over-voltages have been analysed. The program achieves mostly a good description of the spectra, and the parameters determined agree with the values from the producers.The program can be used for detailed analyses of single spectra, but, as it is compatible with the native Python multiprocessing module, also for the automatic characterisation of large samples of SiPMs.

Approaching pixel-level readout of SNSPD array by inductor-shaping pulse

Although many multiplexed arrays of a superconducting nanowire single-photon detector (SNSPD) have been reported, it is still a major challenge to develop pixel-level readout arrays with high efficiency, parallel detection, and fast processing for real-time imaging. Here, we report a SNSPD array with inductor-shaping pulses for approaching the pixel-level readout. Optimized inductors are introduced to shape the output pulses of each pixel, and the response pulses of all pixels are synthesized in a series-connected structure. Then, the on/off states of all pixels can be encoded to the widths, amplitudes, and areas of the output pulses by the single-channel readout. This proposal is verified by a 4-pixel SNSPD array and a 16-pixel SNSPD array. It shows that the array not only inherits the features of the single-pixel SNSPD, such as photosensitive area, filling factor, quantum efficiency, and dark count rate, but also implements parallel operation of all pixels, which is always confused in traditional multiplexed SNSPD arrays. At the same time, the single-channel readout simplifies the system, and the serial digital signal converted from the shaped pulse enabled an easy and fast readout process, paving the way for high performance and real-time imaging.

Fast time-domain diffuse correlation spectroscopy with superconducting nanowire single-photon detector: system validation and in vivo results

Time-domain diffuse correlation spectroscopy (TD-DCS) has been introduced as an advancement of the “classical” continuous wave DCS (CW-DCS) allowing one to not only to measure depth-resolved blood flow index (BFI) but also to extract optical properties of the measured medium without using any additional diffuse optics technique. However, this method is a photon-starved technique, specially when considering only the late photons that are of primary interest which has limited its in vivo application. In this work, we present a TD-DCS system based on a superconducting nanowire single-photon detector (SNSPD) with a high quantum efficiency, a narrow timing response, and a negligibly low dark count noise. We compared it to the typically used single-photon avalanche diode (SPAD) detector. In addition, this system allowed us to conduct fast in vivo measurements and obtain gated pulsatile BFI on the adult human forehead.