Dark Count Noise Research Articles

Characterization of intrinsic radiation in LYSO scintillators using GEANT4 and SimSiPM simulations.

The intrinsic radiation spectra of LYSO scintillators are investigated through detailed GEANT4 and SimSiPM simulations, focusing on how changes in configuration and size influence the radiation characteristics. Using these simulation packages together, a comprehensive simulation of the physical processes as well as a detailed simulation of the photodetector response, including factors such as dark count rate, optical crosstalk, afterpulse, noise, and saturation effects, was performed. The results of the simulations indicate that the primary factor affecting the intrinsic radiation pattern is the total volume of the crystal, rather than surface treatments or minor geometric variations. The consistency between GEANT4 and SimSiPM simulations confirms the validity of using these simulation methods to analyze the spectral behavior of LYSO scintillators detailed in various applications such as positron emission tomography and nuclear spectroscopy.

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

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.

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.

Signal processing to reduce dark noise impact in precision timing

We introduce a technique to mitigate the effects of low frequency noise on precision timing.The example of Dark Count Noise Rate (DCR) in Silicon Photomultipliers (SiPMs) is emphasized.This technique exploits the correlation between time shifts onthe leading edge of a signal and the residual slope of the baseline (due to noise) which remainsafter baseline subtraction. In fast timing applications (such as for Time-of-flight particle ID) the signal arrival time is typically captured on the signal leading edge. The signal risetime is often fixed by the physics of the sensor and input circuit. Then accurate pulse timing can be achieved by correcting a leading edge threshold time (depending on a slope proportional to both the Amplitude and the risetime) to a “constant fraction” time. This compensation for time walk due to amplitude fluctuations breaks down once we introduce interference from low frequency noise on the leading edge. In this paper we demonstrate that an additional measurement of the slope at threshold can be used to correct for this noise jitter.

Proposal for a long-distance nonlocality test with entanglement swapping and displacement-based measurements

We analyze an all-optical setup which enables Bell-inequality violation over long distances by exploiting probabilistic entanglement swapping. The setup involves only two-mode squeezers, displacements, beamsplitters, and on-off detectors. We describe how events must be arranged to close both the detection and locality loopholes. We analyze a scenario with dichotomic inputs and outputs, and check the robustness of the Bell inequality violation for up to six parties, with respect to phase, amplitude, and dark count noise, as well as loss.

Layered CMOS SPADs for Low Noise Detection of Charged Particles

This paper reports the characterization of SPAD arrays fabricated in a 150 nm CMOS technology in view of applications to the detection of charged particles. The test vehicle contains SPADs with different active area and operated with different quenching techniques, either passive or active. The set of devices under test (DUTs) consists of single-tier chips, about 30 mm2 in area, with dual-tier structures where two chips are face-to-face bump bonded to each other. In the dual-layer structure obtained in this way, the coincidence signal between overlapping SPAD pairs is read out, with a beneficial impact on the dark count noise performance. The DUT characterization was mainly focused on studying the breakdown voltage in the single-layer arrays and the dark count rate (DCR), measured in different working conditions, in both the single- and the dual-layer structures. Comparison between the DCR performance of the two configurations clearly emphasizes the advantage of the coincidence readout architecture.

An Accurate Circuit Model for the Statistical Behavior of InP/InGaAs SPAD

In the field of near-infrared weak light detection, an InP/InGaAs single-photon avalanche diode (SPAD) is preferred due to the advantages of high sensitivity, low cost and room-temperature operation. To properly simulate and optimize the SPAD’s front-end circuit, a comprehensive and compact behavior model of the InP/InGaAs SPAD is normally required to accurately describe the statistical behavior of the detectors. In this paper, an InP/InGaAs SPAD analytical model is constructed, which not only includes the direct current (DC) and alternating current (AC) behavior simulating the avalanche and quenching processes, but also describes the dark count, after-pulsing and photon detection efficiency. For dark count noise, three important generation mechanisms are considered, including thermal generation, trap-assisted tunneling and band-to-band tunneling. The model described by the Verilog-A hardware description language (HDL) can be directly implemented in the commercial circuit simulator. A gated mode, passive quenching and recharging circuit is used to simulate and verify the developed model. The simulation results are in good agreement with the reported test data, demonstrating the accuracy of the developed InP/InGaAs SPAD model.

Experimental method to monitor temperature stability of SiPMs operating in conditions of extremely high dark count rate

The use of Silicon Photomultipliers (SiPMs) in high radiation environments (e.g. detectors at collider experiments) or in outdoor conditions (e.g. LIDAR applications), requires to deal with a high level of dark count noise. An undesired effect emerging under these conditions is the self-heating of the SiPM due to a large power dissipation that causes variations of the breakdown voltage and thus affects operating parameters such as gain and PDE. A method to evaluate the heat dissipation properties of different SiPM packages and the temperature stability of SiPMs during operation under extremely high dark count rates (larger than 30 GHz) is presented in this paper. Starting from a condition in which the SiPM is at thermal equilibrium with the environment, a change in the current measured under intense illumination with a LED can be attributed to a temperature variation of the SiPM due to self-heating. Under certain assumptions, a quantitative estimate of the local change of temperature can be obtained if certain parameters of the SiPM are known: gain, photon detection efficiency, equivalent charge factor and drift of the SiPM breakdown voltage with temperature. The method is applied to evaluate the thermal conductivity of different SiPM package configurations, which is a key requirement for reliable operation in conditions of extremely high dark count rate. Among the SiPM package configurations tested, the one consisting of a ceramic substrate coupled to a copper heat sink provided the best performance in terms of good heat dissipation with less than 0.5 °C temperature variation for 100 mW dissipated power.

A scalable single-photon avalanche diode with improved photon detection efficiency and dark count noise

An improved scalable single-photon avalanche diode (SPAD) structure with a virtual epitaxial guard ring is presented based on a Bipolar-CMOS-DMOS (BCD) technology. A deep junction between the P-well and the medium-voltage N-well (MVNW) is devised as the avalanche region for the improvement of photon detection efficiency (PDE) and spectral response. Moreover, an N+ buried layer is adopted to enable substrate isolation for the reduction of electrical crosstalk and the facilitation of pixel integration. In particular, a lower doped p-type epitaxial layer is used as a virtual guard ring, which can effectively suppress the dark count rate (DCR) induced by STI-interface traps. The modeling and simulation results indicate that, compared to the P+/P-well/Deep N-well (PWDN) SPAD, the proposed device structure achieves a higher PDE in a wider spectral range, meanwhile, the DCR is also greatly reduced.

Digitized waveform signal processing for fast timing: an application to SiPM timing in the presence of dark count noise

In this paper we illustrate techniques for digitized waveform signal processing of fast timing detectors. In the example discussed here, timing analysis of SiPM signals in the presence of high Dark Count Rates, a large data set of digitized waveforms is used to develop an optimal strategy relevant to the electronics front end design.

Reducing dark count of single-photon avalanche diode detector with polysilicon field plate

To suppress the effect of dark count noise on single photon avalanche diode (SPAD) detector, the mechanism and method of reducing the dark count rate (DCR) of SPAD device by using a polysilicon field plate is studied in this paper. Based on the 0.18-μm standard CMOS process, a polysilicon field plate located between the P+ active region and shallow trench isolation (STI) is deposited to reduce the dark count noise for a scaleable P+/P-well/deep N-well SPAD structure. Test results show that the DCR of SPAD device decreases by an order of magnitude after the deposition of polysilicon field plates, and its dark count performance at high temperature is even better than that of device without polysilicon field plate at room temperature. The TCAD simulation further indicates that the peak electric field in the guard ring region of the SPAD device is introduced into the STI by the field plate, and the overall electric field in the guard ring region is reduced by 25%. Finally, through modeling and calculating the DCR, the polysilicon field plate weakens the electric field of the guard ring region with high trap density, hence the trap-related DCR is significantly reduced. Therefore, the dark count performance of SPAD detector is effectively improved.

Ultraviolet beam splitter characterization for use in a CubeSat optical system

The U.S. Naval Research Laboratory (NRL) has developed the Triple Tiny Ionospheric Photometer (Tri-TIP), an ultraviolet remote-sensing instrument based on the TIP. Tri-TIP measures emissions of atomic oxygen (O i 135.6 nm) to determine plasma density in the nighttime ionosphere. The Tri-TIP design shrinks TIP to a 1U CubeSat form-factor and simplifies the mechanical design with a three-channel photometer system to isolate the target wavelength without a filter wheel. A heated strontium fluoride (SrF2) filter eliminates incoming light at wavelengths shorter than 135.6 nm. The filtered light is divided between two matched photometers by a beam splitter with a magnesium fluoride coating over aluminum (AlMgF2) deposited on 50% of the surface in a polka-dot pattern. The third photometer monitors dark count noise for later subtraction. One Tri-TIP configuration uses a beam splitter with a sapphire (Al2O3) substrate, which is opaque to wavelengths shorter than ∼140 nm, to later subtract contaminating emissions at wavelengths longer than 140 nm. A second Tri-TIP configuration uses a MgF2 substrate beam splitter to simultaneously measure O i 135.6 nm from two adjacent fields-of-view. The performance of both beam splitters has been tested at NRL, and the results are presented.

An accurate behavioral model for single-photon avalanche diode statistical performance simulation

An accurate behavioral model is presented to simulate important statistical performance of single-photon avalanche diodes (SPADs), such as dark count and after-pulsing noise. The derived simulation model takes into account all important generation mechanisms of the two kinds of noise. For the first time, thermal agitation, trap-assisted tunneling and band-to-band tunneling mechanisms are simultaneously incorporated in the simulation model to evaluate dark count behavior of SPADs fabricated in deep sub-micron CMOS technology. Meanwhile, a complete carrier trapping and de-trapping process is considered in afterpulsing model and a simple analytical expression is derived to estimate after-pulsing probability. In particular, the key model parameters of avalanche triggering probability and electric field dependence of excess bias voltage are extracted from Geiger-mode TCAD simulation and this behavioral simulation model doesn't include any empirical parameters. The developed SPAD model is implemented in Verilog-A behavioral hardware description language and successfully operated on commercial Cadence Spectre simulator, showing good universality and compatibility. The model simulation results are in a good accordance with the test data, validating high simulation accuracy.

Micro-pulse polarization lidar at 1.5 μm using a single superconducting nanowire single-photon detector.

An all-fiber, eye-safe and micro-pulse polarization lidar is demonstrated with a polarization-maintaining structure, incorporating a single superconducting nanowire single-photon detector (SNSPD) at 1.5μm. The time-division multiplexing technique is used to achieve a calibration-free optical layout. A single piece of detector is used to detect the backscatter signals at two orthogonal states in an alternative sequence. Thus, regular calibration of the two detectors in traditional polarization lidars is avoided. The signal-to-noise ratio of the lidar is guaranteed by using an SNSPD, providing high detection efficiency and low dark count noise. The linear depolarization ratio (LDR) of the urban aerosol is observed horizontally over 48h in Hefei [N31°50'37'', E117°15'54''], when a heavy air pollution is spreading from the north to the central east of China. Phenomena of LDR bursts are detected at a location where a building is under construction. The lidar results show good agreement with the data detected from a sun photometer, a 532nm visibility lidar, and the weather forecast information.

Dual-frequency Doppler lidar for wind detection with a superconducting nanowire single-photon detector.

A dual-frequency direct detection Doppler lidar is demonstrated using a superconducting nanowire single-photon detector (SNSPD) at 1.5μm. The so-called double-edge technique is implemented by using a dual-frequency laser pulse, rather than using a double-channel Fabry-Perot interferometer. Such a modification to the reported lidars enhances the frequency stability in the system level. Using the time-division multiplexing method, only one piece of SNSPD is used in the optical receiver, making the system simplified and robust. The SNSPD is adopted to enhance the temporal resolution since it offers merits of high quantum efficiency, low dark count noise, no after-pulsing probability, and a high maximum count rate. Two telescopes that point westward and northward at a zenith angle of 30° are used to detect the line-of-sight wind components, which are used to synthesize the horizontal wind profile. Horizontal wind profiles up to an altitude of about 2.7km are calculated with vertical spatial/temporal resolution of 10m/10s. Wind dynamic evolution and vertical wind shears are observed clearly.

Comprehensive understanding of dark count mechanisms of single-photon avalanche diodes fabricated in deep sub-micron CMOS technologies

The dark count noise mechanisms of single-photon avalanche diodes (SPADs) fabricated in deep sub-micron (DSM) CMOS technologies are investigated in depth. An electric field dependence of tunneling model combined with carrier thermal generation is established for dark count rate (DCR) prediction. Applying the crucial parameters provided by Geiger mode TCAD simulation such as avalanche triggering probability and electric field distribution in the SPAD avalanche region, the individual contribution of each noise source to DCR is calculated for several SPADs in DSM CMOS technologies. The model calculation results reveal that the trap-assisted tunneling is the main DCR generation source for these DSM CMOS SPADs. With the increase of doping levels in the device avalanche region, the band-to-band tunneling will be the dominant factor that could lead to the higher DCR in scaled DSM CMOS technologies.

Development of a 64-Channel Readout ASIC for an SSPM Array for PET and TOF-PET Applications

In this paper, we developed a 64-channel application specific integrated circuit (ASIC) named EXYT for $8 \times 8$ SSPM arrays for positron emission tomography (PET) and time-of-flight (TOF)-PET applications. It integrates individual fast readout for timing and resistive networks for energy and position measurements, which reduces the outputs down to 4 differential signals: Timing, Energy and X/Y positions. Gated summation circuits were implemented to suppress the dark count noise and to reduce the dead time. An automatic threshold calibration method was also introduced in this paper and the threshold difference among all the channels could be effectively reduced to $ . by adjusting a local 5-bit DAC for each channel. The chip has been fabricated with $0.18\,\mu\text{m}$ CMOS technology. Evaluation system with SSPM array and LYSO crystals has been developed. All the functions of EXYT have been tested and verified. The power consumption is 3 mW per channel. Energy resolution of 12% and coincidence resolving time (CRT) of 363 ps (FWHM–full width at half maximum) have been achieved for $2 \times 2 \times 14\, \text{mm}^3$ LYSO crystal(s). Sub-pixel resolution can be achieved when coupled to a $12 \times 12$ array of $2.7 \times 2.7 \times 14\, \text{mm}^3$ LYSO crystals.

Optimization of a heralded single-photon source with spatial and temporal multiplexing

The properties of a heralded single-photon source with temporal and spatial multiplexing are studied with the aim to maximize its efficiency for a given value of the second-order zero-time autocorrelation function. We show that the variable time delay, which is used for temporal multiplexing, can be optimized so that the mean number of photon passes through the switches and the total number of switches are respectively reduced to ∼ log2N and ∼ (1/2)log2N, where N is the temporal multiplexing degree. The total efficiency of such an optimized source is calculated for typical switching losses and the autocorrelation function is calculated in the presence of the detector dark-count noise.

WDM-PON Monitoring With Tunable Photon Counting OTDR

We explore the performance of a tunable optical time domain reflectometer based on single photon detection for fault location and quantification in wavelength division multiplexing (WDM)-passive optical networks based on a 32-channel cyclic arrayed waveguide grating using the S- and C -bands for upstream (156 Mb/s) and downstream (2.5 Gb/s) transmission and the L -band for monitoring. Downstream Rayleigh and Raman scattering contributions to the dark count noise were evaluated and properly filtered out with a total WDM + filter rejection ratio of 90 dB. Upstream power was found to generate the greatest contribution to the noise floor and is the limiting factor to the upstream transmission data rate. In-service monitoring experiments with full upstream and downstream power show that the proposed scheme is able to achieve dynamic range levels of up to 32 dB with 5-m spatial resolution and no measurable penalty in data transmission.