Low Dark Count Rate Research Articles

Superconducting nanowire single photon detector at 532 nm and demonstration in satellite laser ranging.

Superconducting nanowire single-photon detectors (SNSPDs) at a wavelength of 532 nm were designed and fabricated aiming to satellite laser ranging (SLR) applications. The NbN SNSPDs were fabricated on one-dimensional photonic crystals with a sensitive-area diameter of 42 μm. The devices were coupled with multimode fiber (ϕ = 50 μm) and exhibited a maximum system detection efficiency of 75% at an extremely low dark count rate of <0.1 Hz. An SLR experiment using an SNSPD at a wavelength of 532 nm was successfully demonstrated. The results showed a depth ranging with a precision of ~8.0 mm for the target satellite LARES, which is ~3,000 km away from the ground ranging station at the Sheshan Observatory.

Gigacount/second Photon Detection Module Based on an 8 × 8 Single-Photon Avalanche Diode Array.

In this letter we present a compact photon detection module, based on an 8×8 array of single-photon avalanche diodes (SPADs). The use of a dedicated silicon technology for the fabrication of the sensors allows us to combine large active areas (50-μm diameter), high photon detection efficiency (49% at 550-nm wavelength) and low dark count rate. Thanks to a fully parallel architecture, the module provides voltage pulses synchronous to each photon detection for a maximum global count rate exceeding 1 Gcps. These properties makes the system suitable for operation in two different free-running modes. The first, suitable to acquire faint signals, allows multi-spot acquisitions and can be used to considerably reduce the measurement time in applications like single-molecule analysis. With the second it is possible to use all the pixels in a combined mode, to extend and move the dynamic range of the module to very high count rates and to attain number resolving capabilities.

Broadband Near-Infrared Superconducting Nanowire Single-Photon Detector with Efficiency over 50%

We report a broadband superconducting nanowire single-photon detector for the near-infrared waveband. The optical absorptance in this band is enhanced by utilizing a reflective aluminum mirror and a SiO2 layer as an optical cavity. A broadband system detection efficiency (SDE) over 50% from 950 to 1600 nm with a low dark count rate of 10 Hz is realized by coupling a HI 1060 FLEX single-mode fiber. The SDE s reaches 78.3%, 70.9%, and 57.7% at the wavelengths of 1064, 1310, and 1550 nm, respectively. A system timing resolution (jitter) of 83 ps at 1550 nm is obtained. The detector may be useful for broadband applications such as earth observation, environment monitoring, and biomedicine.

Enhanced laser ranging with superconducting nanowire single photon detector for low dark count rate

Superconducting nanowire single photon detector (SNSPD) is a competitive candidate in laser ranging at 1064 nm wavelength compared with other single photon detectors such as InGaAs/InP APD for its high sensitivity, high time precision and low dark counts. In this paper, we apply our SNSPD to a laser ranging system measuring target in Qinghai lake area with atmospheric scatter. The echo photons are received by telescope, and transport through the multimode fiber to the SNSPD photon-sensitive area. The SNSPD, integrated in an optical cavity with a resonant wavelength of 1064 nm, is fabricated on a MgF2 substrate. The optical absorption of NbN film goes up to 98% according to FDTD simulation, and the system efficiency is measured to be about 40%. A pulsed laser at 1064 nm, featuring a peak power of 12 MW and a pulse width of 10 ns, is adopted in the laser ranging system. In this experiment, we first measure the system intrinsic noise and the environment noise introduced into the laser ranging system after turning off the laser. After that, we measure the echo rate for the target at 126 km, which increases up to 96% with an attenuator of 10 dB at the receiver side. The maximum distance of the laser ranging system is analyzed based on the experimental results of dark count and echo rate through a theoretical model of laser radar. The analysis indicates that signal-to-noise ratio (SNR) is increased smoothly with the accumulation of time. At the same time, we simulate how the dark counts influence the capability of laser ranging system based on SNSPD, the simulated SNR matches well with the experimental data of target at 126 km. Furthermore, the dark counts, accumulation of time and probability of echo photon affect the SNR according to the simulation results, showing that large dark counts would result in SNR fluctuation and signal annihilation when the probability of echo photon is low. Thus, the maximum distance of laser ranging under the assumption of integration time is estimated through the SNR simulated result, showing that a maximum distance is up to 280 km, 40 km far away from APD detector based system under the same conditions mainly due to the very low dark counts of SNSPD. It should be pointed out that the coupling efficiency between SNSPD and the receiving telescope is low for small view field limited by the 62.5 m fiber of SNSPD. Thus, further work is to fabricate SNSPD with a larger coupling area which is possible to increase the maximum distance with improved coupling settings.

A compact, high-density gamma-detection module for Time-of-Flight measurements in PET applications

We present a very compact γ-detection module primarily designed for PET applications. On a total area of about 30×30mm2, 144 SiPM photodetectors coupled to scintillator crystals are read out individually with fast timing ASICs. The core of the module is a LTCC ceramic substrate with internal water channels for efficient and stable liquid cooling. The top side of the LTCC is covered by 12×12 SiPMs in a regular pitch of 2.5mm. The SiPMs are designed in the RGB-HD technology from FBK with a single cell size of 25×25μm2, very low dark-count rate and stable performance over a wide temperature range from 0 to 20°C. The readout of the SiPMs is done with 4 specialized PETA5 ASICs flip-chip mounted to the bottom side of the substrate. Each chip has 36 readout channels (available in single or differential ended configuration) with self-triggered hit detection, a very low noise discriminator, signal amplitude integration and digitization, a TDC with 50ps binwidth, neighbor logic and fast veto mechanisms. The full height of the assembly, including the connector to the main readout board, is less than 1cm. In a 1:1 coupling configuration with 10mm high LYSO scintillator arrays for detection of 511keV gammas, the module has already reached 205ps CRT time resolution (FWHM in coincidence between channels on two different modules), sufficient for ToF operation in PET. The module design, details on chip operation and latest results with LYSO arrays are described.

Superconducting single-photon detectors integrated with diamond nanophotonic circuits

Photonic quantum technologies promise to repeat the success of integrated nanophotonic circuits in non-classical applications. Using linear optical elements, quantum optical computations can be performed with integrated optical circuits and thus allow for overcoming existing limitations in terms of scalability. Besides passive optical devices for realizing photonic quantum gates, active elements such as single photon sources and single photon detectors are essential ingredients for future optical quantum circuits. Material systems which allow for the monolithic integration of all components are particularly attractive, including III-V semiconductors, silicon and also diamond. Here we demonstrate nanophotonic integrated circuits made from high quality polycrystalline diamond thin films in combination with on-chip single photon detectors. Using superconducting nanowires coupled evanescently to travelling waves we achieve high detection efficiencies up to 66 % combined with low dark count rates and timing resolution of 190 ps. Our devices are fully scalable and hold promise for functional diamond photonic quantum devices.

Ultrafast superconducting single-photon detector with a reduced active area coupled to a tapered lensed single-mode fiber

This paper presents an ultrafast niobium nitride (NbN) superconducting single-photon detector (SSPD) with an active area of 3×3 μ m 2 that offers better timing performance metrics than the previous SSPD with an active area of 7×7 μ m 2 . The improved SSPD demonstrates a record timing jitter ( ), an ultrashort recovery time ( ), an extremely low dark count rate, and a high detection efficiency in a wide spectral range from visible part to near infrared. The record parameters were obtained due to the development of a new technique providing effective optical coupling between a detector with a reduced active area and a standard single-mode telecommunication fiber. The advantages of the new approach are experimentally confirmed by taking electro-optical measurements.

Method to evaluate afterpulsing probability in single-photon avalanche diodes.

We propose and demonstrate a new method for evaluating the afterpulsing effect in single-photon avalanche photodiodes (SPADs). By analyzing the statistical property of dark count rate, we can quantitatively characterize afterpulsing probability (APP) of a SPAD. In experiment, the temperature-dependent low dark count rate (DCR) distribution becomes non-Poissonian at lower temperature and has higher excess bias as the afterpulsing effect becomes significant. Our work provides a flexible way to examine APP in either single-device or circuit level.

Ultimate low system dark-count rate for superconducting nanowire single-photon detector.

The dark-count rate (DCR) is a key parameter of single-photon detectors. By introducing a bulk optical band-pass filter mounted on a fiber-to-fiber optical bench cooled at 3 K and blocking down to 5 μm, we suppressed the DCR of a superconducting nanowire single-photon detector by more than three orders of magnitude. The DCR is limited by the blackbody radiation through a signal passband of 20-nm bandwidth. The figure of merit, system detection efficiency, and DCR were 2.7×10(11), 2.3%, and 10(-3) Hz, respectively. Narrowing the bandwidth to 100 GHz suppresses the DCR to 10(-4) Hz, and the figure of merit increases to 1.8×10(12).

High-Fill-Factor &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$60\times 1$ &lt;/tex-math&gt;&lt;/inline-formula&gt; SPAD Array With 60 Subnanosecond Integrated TDCs

This letter presents a high-fill-factor $60\,\, \times \,\, 1$ linear array of single-photon avalanche diodes (SPADs) and 60 integrated time-to-digital converters (TDCs). The 100- $\mu \text{m}$ diameter SPAD has high photon detection efficiency (50% at 420 nm), very low dark count rate (2.5 kcps at room temperature), and negligible crosstalk ( $\sim 0.1$ % between adjacent pixels). The TDC resolution is 250 ps and its single-shot precision of 200-ps rms is limited just by the quantization noise. Very good linearity ( ${\rm DNL}=5{\%}$ LSB rms and ${\rm INL}=30{\%}$ LSB rms ) is achieved because of the sliding scale technique. The overall fill-factor of the array is 52%. This chip is suitable for many advanced spectroscopic applications, since it provides 60 independent single-photon detectors and the corresponding counting and timing electronics within just one integrated circuit.

Afterpulsing studies of low-noise InGaAs/InP single-photon negative-feedback avalanche diodes

We characterise the temporal evolution of the afterpulse probability in a free-running negative-feedback avalanche diode (NFAD) over an extended range, from ns to ms. This is possible thanks to an extremely low dark count rate on the order of 1 cps at 10% efficiency, achieved by operating the NFAD at temperatures as low as 143 K. Experimental results in a large range of operating temperatures (223–143 K) are compared with a legacy afterpulsing model based on multiple trap families at discrete energy levels, which is found to be lacking in physical completeness. Subsequently, we expand on a recent proposal which considers a continuous spectrum of traps by introducing well-defined edges to the spectrum, which are experimentally observed.

Materials Development for High Efficiency Superconducting Nanowire Single-Photon Detectors

ABSTRACTSuperconducting nanowire single-photon detectors (SNSPDs) based on ultra-thin films have become the preferred technology for applications that require high efficiency single-photon detectors with high speed, high timing resolution, and low dark count rates at near-infrared wavelengths. Since demonstration of the first SNSPD using NbN thin films, an increasingly larger number of materials are being explored. We investigate amorphous thin film alloys of MoSi, MoGe, and WRe with the goal of optimizing SNSPDs for higher operating temperature, high efficiency and high speed. To explore material adequacy for SNSPDs, we have measured superconducting transition temperature (Tc) as a function of film thickness and sheet resistance, as well as critical current densities. In this paper we present our results comparing these materials to WSi, another amorphous material widely used for SNSPD devices.

EUV emissions from solar wind charge exchange in the Earth's magnetosheath: Three‐dimensional global hybrid simulation

AbstractIn this paper, a three‐dimensional (3‐D) global hybrid simulation code and a 3‐D geocoronal hydrogen model are used to systematically study the extreme ultraviolet (EUV) emissions at 30.4 nm produced by solar wind charge exchange (SWCX) in the Earth's magnetosheath, associated with different solar wind‐interplanetary magnetic field (SW‐IMF) conditions and different imaging perspectives. We have found that the EUV emission intensities in the magnetosheath are highly variable from several mR to ~1200 mR and increase with the flow speed, the density, the temperature, and the He2+/H+ density ratio of the solar wind; the northward IMF leads to a minimum emission in the magnetosheath, whereas the southward IMF generates a maximum emission; with the increase of the magnitude of IMF, the emission pattern in the nightside splits from single field‐aligned shape into a butterfly shape around the magnetic equator; and the EUV emissions vary with the imaging positions, reflecting different latitudinal and longitudinal information of the magnetosheath. It is noted that the SWCX EUV emissions in the magnetosheath for highly disturbed solar wind conditions should be considered in processing the Moon‐based plasmaspheric EUV images. We suggest that EUV imaging of the global magnetosheath requires an EUV imager with large field‐of‐view, high‐sensitivity, large dynamic range, and low intrinsic dark count rate. This investigation could provide us with an overall understanding on SWCX EUV emissions in the magnetosheath which can potentially be used to image the global magnetosheath to study the solar wind‐magnetosphere coupling in the future.

SPAD array chips with full frame readout for crystal characterization

We present single photon sensitive 2D camera chips containing 88x88 avalanche photo diodes which can be read out in full frame mode with up to 400.000 frames per second. The sensors have an imaging area of ~5mm x 5mm covered by square pixels of ~56µm x 56µm with a ~55% fill factor in the latest chip generation. The chips contain a self triggering logic with selectable (column) multiplicities of up to >=4 hits within an adjustable coincidence time window. The photon accumulation time window is programmable as well. First prototypes have demonstrated low dark count rates of <50kHz/mm2 (SPAD area) at 10 degree C for 10% masked pixels. One chip version contains an automated readout of the photon cluster position. The readout of the detailed photon distribution for single events allows the characterization of light sharing, optical crosstalk etc., in crystals or crystal arrays as they are used in PET instrumentation. This knowledge could lead to improvements in spatial or temporal resolution.

Characterization of the Hamamatsu MPPC S11834 as photon sensor for RICH

Recent development of SiPMs makes them a promising candidate for replacement of photomultiplier tubes in Ring Imaging Cherenkov (RICH) counters. A commercially available 8×8 SiPM array, Hamamatsu MPPC S11834 with a rather low dark count rate, was tested as a single photon sensor in a RICH counter. To increase its overall geometrical acceptance, light concentrators were employed. The various factors that influence their efficiency are estimated and the results of measurements with polarized light are presented, showing a good agreement with a Monte Carlo study.

Low-Noise, Low-Jitter, High Detection Efficiency InGaAs/InP Single-Photon Avalanche Diode

We present the performance of a novel InGaAs/InP single-photon avalanche diode (SPAD) with high detection efficiency and low noise thanks to the improvement of Zinc diffusion conditions and the optimization of the vertical structure. The 25-μm active-area diameter detector, operated in gated-mode with ON time of tens of nanoseconds, shows very low dark count rate (few kilo-counts per second at 225 K and 5 V of excess bias), 30% photon detection efficiency at 1550 nm, low afterpulsing, and a timing response with less than 90-ps full-width at half maximum and very fast exponential tail (time constant ~ 60 ps). Therefore, this InGaAs/InP SPAD is among the best ones ever reported in the literature.

Radiometric temperature measurement with Si and InGaAs single-photon avalanche photodiode.

We experimentally demonstrate the use of single-photon avalanche photodiode (SPAD) for radiometric temperature measurement. The low dark count rate CMOS SPAD and a commercial InGaAs/InP SPAD can detect the thermal radiation from a blackbody down to the temperatures of 510 and 405 K, respectively. Our work shows that current SPADs are cost-effective thermal sensors for various applications.

Characterization of the current-induced resistive spots in superconducting $$\hbox {YBa}_{2} \hbox {Cu}_{3} \hbox {O}_{7}$$ YBa 2 Cu 3 O 7 strips

For over a decade, ultrathin superconducting films have been developed for the detection of single photons at optical or near infrared frequencies, with competitive performances in terms of quantum efficiency, speed, and low dark count rate. In order to avoid the requirement of helium refrigeration, we consider here the use of high temperature materials, known to achieve very fast responsiveness to laser irradiation. We excite thin filaments of the cuprate $$\hbox {YBa}_{2} \hbox {Cu}_{3} \hbox {O}_{7}$$ by rectangular pulses of supercritical current so as to produce either a phase-slip centre (PSC) or a normal hot spot (HS), according to the temperature and the current amplitude selected. That procedure provides information about the maximum bias current to be used in a particle detector, about the return current back to the quiescent state after excitation, and about the rate of growth and decay of a HS. We also measure the time of PSC nucleation. A unique feature of that approach is to provide the rate of heat transfer between the film and its substrate at whatever temperature, in the superconducting state, in the practical conditions of operation.

Test of the Hamamatsu MPPC module S11834 as a RICH photon detector

In our previous studies, we have shown that silicon photo-multipliers can be used as single photon detectors in a RICH counter (Korpar et al., 2009, 2010 [1,2]). Their main advantage with respect to the classical photo-multiplier tubes is the operation in high magnetic fields, while their disadvantage is a relatively high dark count rate. Recently, Hamamatsu made commercially available sensors with a rather low dark count rate (≈0.1MHz/mm2) and with a larger active area, offering a possibility for a much better signal-to-noise ratio. We have designed, constructed and tested a module with Hamamatsu 8×8 channel S11834 MPPCs. To increase the geometric acceptance, light concentrators have been employed. In the present contribution we discuss the results of studies of the light concentrator design optimization and of the detector module response to fast light pulses. Also presented are the results of RICH prototype tests in a test beam.

Analysis of InGaAs/InP Single-Photon Avalanche Diodes With the Multiplication Width Variation

This letter investigates dependence of performances of single-diffused single-photon avalanche photodiodes (SPADs) using a wet recess-etching technique on a multiplication width. Three-types of single-diffused InGaAs/InP planar SPADs with the different multiplication width have been fabricated and analyzed, which have no diffusion depth variation between fabricated devices. The fabricated SPAD with the multiplication width of 1.3 μm shows a low dark count rate (DCR) of 9 kHz with a photon detection efficiency of 17.1% at 240 K. It is found that the DCR is reduced by increasing the multiplication width.