Geiger-mode Avalanche Photodiodes Research Articles

A Real-Time Restraint Method for Range Walk Error in 3-D Imaging Lidar Via Dual Detection

Geiger-mode avalanche photodiode (Gm-APD) offers 3D imaging lidar much better capability in terms of detection sensitivity. However, a range walk error (RWE) exists in Gm-APDs which refers to the fluctuation of the measured distance as a function of the intensity of echo pulses. In this paper, we present a real-time restraint method for RWE implemented by unequally intensity-dividing the echo pulses into two Gm-APDs. The difference image of two depth images measured by the divided beams is a matrix of RWE distribution and the intensity image is used to censor the anomalous pixels in the matrix. Combined with the matrix of RWE distribution, an accurate depth image with low RWE can be obtained. Experimental results demonstrate that the proposed method reduces approximately 86% RWE of the conventional method in real time.

Influence investigation on ranging performance for range-gated Geiger-mode avalanche photodiode ladar.

The ranging performance for Geiger-mode avalanche photodiode (Gm-APD) laser detection and ranging (ladar) is mainly evaluated by range accuracy and precision; although Gm-APD ladar can evaluate the ranging performance of the exact position, it is not helpful to comprehensively evaluate the influence on the ranging of each parameter in the whole gate. Due to the target echo's stochastic trigger making the delay adjustment inaccurate, the position of the echo in the gate is stochastic in the actual detection process, so the theoretical calculation may not be able to make ladar ranging performance clear. As to this question, based on the central limit theorem, and assuming the position of the target in the gate obeys Gaussian distribution, while also combining the Gm-APD triggering probability model, we propose the mean ranging accuracy and precision theory to objectively evaluate the ranging performance. At the same time, we combine the theory with the ladar ranging equation to investigate the effect of parameters such as laser transmitting energy, pulse width, gate width, target range, and noise intensity on ranging performance. The results show high transmitting energy, narrow gate width, short target range, and low noise intensity make mean ranging accuracy and precision low. The narrow pulse width will result in lower mean ranging accuracy and high mean ranging precision. Wide pulse width has the opposite effect; through comprehensive comparison, 10∼30 ns pulse width is more reasonable. According to theoretical analysis results, to achieve ladar's high ranging performance, we put forward concrete measures for improvement-reducing the gate width, enhancing laser energy, using a narrowband filter to reduce false alarm of noise, etc., consequently the research in this paper has significance for the Gm-APD ladar experimental parameter selection.

Large-Format Geiger-Mode Avalanche Photodiode Arrays and Readout Circuits

Over the past 20 years, we have developed arrays of custom-fabricated silicon and InP Geiger-mode avalanche photodiode arrays, CMOS readout circuits to digitally count or time stamp single-photon detection events, and techniques to integrate these two components to make back-illuminated solid-state image sensors for lidar, optical communications, and passive imaging. Starting with 4 × 4 arrays, we have recently demonstrated 256 × 256 arrays, and are working to scale to megapixel-class imagers. In this paper, we review this progress and discuss key technical challenges to scaling to large format.

Adaptive aperture for Geiger mode avalanche photodiode flash ladar systems.

Although the Geiger-mode avalanche photodiode (GM-APD) flash ladar system offers the advantages of high sensitivity and simple construction, its detection performance is influenced not only by the incoming signal-to-noise ratio but also by the absolute number of noise photons. In this paper, we deduce a hyperbolic approximation to estimate the noise-photon number from the false-firing percentage in a GM-APD flash ladar system under dark conditions. By using this hyperbolic approximation function, we introduce a method to adapt the aperture to reduce the number of incoming background-noise photons. Finally, the simulation results show that the adaptive-aperture method decreases the false probability in all cases, increases the detection probability provided that the signal exceeds the noise, and decreases the average ranging error per frame.

基于盖革APD阵列的微扫描激光成像技术

基于盖革APD阵列的微扫描激光成像技术

Improved cumulative probabilities and range accuracy of a pulsed Geiger-mode avalanche photodiode laser ranging system with turbulence effects.

There exists a performance limitation in a pulsed Geiger-mode avalanche photodiode laser ranging system because of the echo intensity random fluctuation caused by turbulence effects. To suppress the influence of turbulence effects, we present a cumulative pulse detection technique with the ability to achieve improved cumulative probabilities and range accuracy. Based on the modulated Poisson model, the cumulative probabilities, range accuracy, and their influencing factors are investigated for a cumulative Q-switched laser pulse train. The results show that the improved cumulative probabilities and range accuracy can be obtained by utilizing cumulative pulse detection, with the condition that the echo intensity is 10, the echo pulse width is 10ns, and the turbulence degree is 3, the target detection probability increases by 0.4, the false alarm probability decreases by 0.08, and the accuracy and precision increase by 46cm and 27cm, respectively.

Optical attenuator for Geiger mode avalanche photodiode laser detection systems

This paper presents a method to estimate the optical attenuator according to the false firing percentage of Geiger Mode Avalanche Photodiode array detection system only under background light. The effect of the dark current and the gate setting are discussed. The efficiency of the Geiger mode avalanche photodiode detection system is improved by the optical attenuator by simulation analysis, that the false probability is reduced in all cases, and the detection probability increases accorindgly when the signal is larger than the total noise. Finally, the imaging simulation experiments show that the average ranging accuracy increase by using optical attenuator.

Influence of dead-time on detection efficiency and range performance of photon-counting laser radar that uses a Geiger-mode avalanche photodiode.

Dead-time has a significant influence on the detection efficiency and range performance of a photon-counting laser radar system with a Geiger-mode avalanche photodiode. In this paper, a rapid universal recursive model of the detection probability of discrete time under various dead-times is proposed, which is verified with controlled parameters. Our model has the advantage of fast computing speed and unifies multi-trigger, single-trigger, and zero-dead-time models. The computing speed is 1 to 2 orders of magnitude faster than Gatt's and Zhao's models under a short dead-time condition, with relative errors less than 0.001 and 10-14, respectively. Subsequently, the detection efficiency and range bias and precision with various dead-times are theoretically calculated and Monte Carlo simulated with different parameters. On the one hand, dead-time shorter than the end time of the target achieves better detection efficiency; however, this results in worse range performance. On the other hand, dead-time longer than the end time of the target maintains the detection efficiency at a low level but provides a better range performance. We discover that noise is the key reason for the periodic fluctuation of the detection efficiency and range performance versus different dead-times and the local optimum values of fluctuations occur when the dead-time is a few nanoseconds shorter or longer than 1, 1/2, 1/3, or even 1/4 of the end time of the target; further, this phenomenon becomes more evident when noise increases. Moreover, weaker noise level is crucial to the detection efficiency, and narrow pulse width and nearer target position in the range gate are important factors to improve precision.

Cumulative detection probabilities and range accuracy of a pulsed Geiger-mode avalanche photodiode laser ranging system

Cumulative pulses detection with appropriate cumulative pulses number and threshold has the ability to improve the detection performance of the pulsed laser ranging system with GM-APD. In this paper, based on Poisson statistics and multi-pulses cumulative process, the cumulative detection probabilities and their influence factors are investigated. With the normalized probability distribution of each time bin, the theoretical model of the range accuracy and precision is established, and the factors limiting the range accuracy and precision are discussed. The results show that the cumulative pulses detection can produce higher target detection probability and lower false alarm probability. However, for a heavy noise level and extremely weak echo intensity, the false alarm suppression performance of the cumulative pulses detection deteriorates quickly. The range accuracy and precision is another important parameter evaluating the detection performance, the echo intensity and pulse width are main influence factors on the range accuracy and precision, and higher range accuracy and precision is acquired with stronger echo intensity and narrower echo pulse width, for 5-ns echo pulse width, when the echo intensity is larger than 10, the range accuracy and precision lower than 7.5 cm can be achieved.

Signal restoration method for restraining the range walk error of Geiger-mode avalanche photodiode lidar in acquiring a merged three-dimensional image.

The fluctuation in the number of signal photoelectrons will cause a range walk error in a Geiger-mode avalanche photodiode (Gm-APD) lidar, which significantly depends on the target intensity. For a nanosecond-pulsed laser, the range walk error of traditional time-of-flight will cause deterioration. A new signal restoration method, based on the Poisson probability response model and the center-of-mass algorithm, is proposed to restrain the range walk error. We obtain a high-precision depth and intensity merged 3D image using this method. The range accuracy is 0.6cm, and the intensity error is less than 3%.

Comparison of flash lidar detector options

Three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks are compared. The tasks are combinations of two collection types (3-D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on Geiger mode avalanche photodiodes (GMAPD), linear mode avalanche photodiodes (LMAPD), and optical time-of-flight lidar, which combine rapid polarization rotation of the image and dual low-bandwidth cameras to generate a 3-D image. We choose scenarios to highlight the strengths and weaknesses of various lidars. We consider HgCdTe and InGaAs variations of LMAPD cameras. The InGaAs GMAPD and the HgCdTe LMAPD cameras required the least energy to 3-D map both scenarios for bare earth, with the GMAPD taking slightly less energy. We comment on the strengths and weaknesses of each receiver technology. Six bits of intensity gray levels requires substantial energy using all camera modalities.

Long-Term Monitoring of Bright Blazars in the Multi-GeV to TeV Range with FACT

Blazars like Markarian 421 or Markarian 501 are active galactic nuclei (AGN), with their jets orientated towards the observer. They are among the brightest objects in the very high energy (VHE) gamma ray regime (>100 GeV). Their emitted gamma-ray fluxes are extremely variable, with changing activity levels on timescales between minutes, months, and even years. Several questions are part of the current research, such as the question of the emission regions or the engine of the AGN and the particle acceleration. A dedicated longterm monitoring program is necessary to investigate the properties of blazars in detail. A densely sampled and unbiased light curve allows for observation of both high and low states of the sources, and the combination with multi-wavelength observation could contribute to the answer of several questions mentioned above. FACT (First G-APD Cherenkov Telescope) is the first operational telescope using silicon photomultiplier (SiPM, also known as Geigermode—Avalanche Photo Diode, G-APD) as photon detectors. SiPM have a very homogenous and stable longterm performance, and allow operation even during full moon without any filter, leading to a maximal duty cycle for an Imaging Air Cherenkov Telescope (IACT). Hence, FACT is an ideal device for such a longterm monitoring of bright blazars. A small set of sources (e.g., Markarian 421, Markarian 501, 1ES 1959+650, and 1ES 2344+51.4) is currently being monitored. In this contribution, the FACT telescope and the concept of longterm monitoring of bright blazars will be introduced. The results of the monitoring program will be shown, and the advantages of densely sampled and unbiased light curves will be discussed.

Boundary evaluation and error correction on pseudo-random spread spectrum photon counting system

The Cramer–Rao lower bound on range error is modeled for pseudo-random ranging systems using Geiger-mode avalanche photodiodes. The theoretical results are shown to agree with the Monte Carlo simulation, satisfying boundary evaluations. Experimental tests prove that range errors caused by the fluctuation of the number of photon counts in the laser echo pulse leads to the range drift of the time point spread function. The function relationship between the range error and the photon counting ratio is determined by using numerical fitting. Range errors due to a different echo energy is calibrated so that the corrected range root mean square error is improved to 1 cm.

Adaptive Target Profile Acquiring Method for Photon Counting 3-D Imaging Lidar

A direct-detection 3-D imaging lidar is capable of acquiring a depth image of noncooperative targets in long distance, using Geiger mode avalanche photodiodes and the technique of time-correlated single-photon counting. However, conventional 3-D imaging lidar has a long data acquisition time. This paper introduces a spatially adaptive method to obtain target profile rapidly for 3-D imaging lidar by exploiting discontinuities between targets and background in the depth domain. The idea behind our strategy is using an adaptive scanning step to localize the regions near the depth boundaries and perform fine scans only to these regions. Fine scans only for those specific regions ensure the recovery accuracy while consuming much less data acquisition time, compared to a conventional high-resolution scanning lidar. Experimental results demonstrate that for the experimental scene, the data acquisition time decreases 85% by using the proposed method, without generating much distortion of the target profile. This method may be of considerable value to fields that need fast 3-D imaging, such as remote sensing and military reconnaissance.

A Readout IC Using Two-Step Fastest Signal Identification for Compact Data Acquisition of PET Systems.

A readout integrated circuit (ROIC) using two-step fastest signal identification (FSI) is proposed to reduce the number of input channels of a data acquisition (DAQ) block with a high-channel reduction ratio. The two-step FSI enables the proposed ROIC to filter out useless input signals that arise from scattering and electrical noise without using complex and bulky circuits. In addition, an asynchronous fastest signal identifier and a self-trimmed comparator are proposed to identify the fastest signal without using a high-frequency clock and to reduce misidentification, respectively. The channel reduction ratio of the proposed ROIC is 16:1 and can be extended to 16 × N:1 using N ROICs. To verify the performance of the two-step FSI, the proposed ROIC was implemented into a gamma photon detector module using a Geiger-mode avalanche photodiode with a lutetium-yttrium oxyorthosilicate array. The measured minimum detectable time is 1 ns. The difference of the measured energy and timing resolution between with and without the two-step FSI are 0.8% and 0.2 ns, respectively, which are negligibly small. These measurement results show that the proposed ROIC using the two-step FSI reduces the number of input channels of the DAQ block without sacrificing the performance of the positron emission tomography (PET) systems.

Universal Performance Prediction for Gated and Free-Running Geiger-Mode Avalanche Photodiodes

This letter proposes a universal discrete-time recurrence (UDR) method to predict the response performance of Geiger-mode avalanche photodiodes (GM-APDs), where performance prediction for a free-running GM-APD is realized beyond the gate-limit assumption for the first time. The dead time effect is summarized as the discrete-time correlation law, and the afterpulsing is first incorporated in the performance prediction theory as an equivalent noise source. Simulations with appropriate parameters verified the high accuracy and low calculation-time requirements of the UDR method.

Development of Gated Pinned Avalanche Photodiode Pixels for High-Speed Low-Light Imaging

This work explores the benefits of linear-mode avalanche photodiodes (APDs) in high-speed CMOS imaging as compared to different approaches present in literature. Analysis of APDs biased below their breakdown voltage employed in single-photon counting mode is also discussed, showing a potentially interesting alternative to existing Geiger-mode APDs. An overview of the recently presented gated pinned avalanche photodiode pixel concept is provided, as well as the first experimental results on a 8 × 16 pixel test array. Full feasibility of the proposed pixel concept is not demonstrated; however, informative data is obtained from the sensor operating under −32 V substrate bias and clearly exhibiting wavelength-dependent gain in frontside illumination. The readout of the chip designed in standard 130 nm CMOS technology shows no dependence on the high-voltage bias. Readout noise level of 15 rms, full well capacity of 8000, and the conversion gain of 75 µV are extracted from the photon-transfer measurements. The gain characteristics of the avalanche junction are characterized on separate test diodes showing a multiplication factor of 1.6 for red light in frontside illumination.

Radiation tolerance of a Geiger-mode avalanche photodiode imaging array

Radiation testing results for a Geiger-mode avalanche photodiode (GM-APD) array-based imager are reviewed. Radiation testing is a crucial step in technology development that assesses the readiness of a specific device or instrument for space-based missions or other missions in high-radiation environments. Pre- and postradiation values for breakdown voltage, dark count rate (DCR), after pulsing probability, photon detection efficiency (PDE), crosstalk probability, and intrapixel sensitivity are presented. Details of the radiation testing setup and experiment are provided. The devices were exposed to a total dose of 50 krad(Si) at the Massachusetts General Hospital’s Francis H. Burr Proton Therapy Center, using monoenergetic 60 MeV protons as the radiation source. This radiation dose is equivalent to radiation absorbed over 10 solar cycles at an L2 orbit with 1-cm aluminum shielding. The DCR increased by 2.3 e−/s/pix/krad(Si) at 160 K, the afterpulsing probability increased at all temperatures and settings by a factor of ∼2, and the effective breakdown voltage shifted by +1.5 V. PDE, crosstalk probability, and intrapixel sensitivity were unchanged by radiation damage. The performance of the GM-APD imaging array is compared to the performance of the CCD on board the ASCA satellite with a similar radiation shield and radiation environment.

Spatial modeling of optical crosstalk in InGaAsP Geiger-mode APD focal plane arrays.

We report a spatial model of optical crosstalk in InGaAsP Geiger-mode APD focal plane arrays created via non-sequential ray tracing. Using twenty-four equivalent experimental data sets as a baseline, we show that experimental results can be reproduced to a high degree of accuracy by incorporating secondary crosstalk effects, with reasonable assumptions of material and emission source properties. We use this model to categorize crosstalk according to source and path, showing that the majority of crosstalk in the immediate neighborhood of avalanching pixels in the present devices can be attributed to direct line-of-sight emissions.

Simulation study of PET detector configuration with thick light guide and GAPD array having large-area microcells for high effective quantum efficiency

Background and ObjectivesLight sharing PET detector configuration coupled with thick light guide and Geiger-mode avalanche photodiode (GAPD) with large-area microcells was proposed to overcome the energy non-linearity problem and to obtain high light collection efficiency (LCE). MethodsA Monte-Carlo simulation was conducted for the three types of LSO block, 4 × 4 array of 3 × 3 × 20 mm3 discrete crystals, 6 × 6 array of 2 × 2 × 20 mm3 discrete crystals, and 12 × 12 array of 1 × 1 × 20 mm3 discrete crystals, to investigate the scintillation light distribution after conversion of the γ-rays in LSO. The incident photons were read out by three types of 4 × 4 array photosensors, which were PSPMT of 25% quantum efficiency (QE), GAPD1 with 50 × 50 µm2 microcells of 30% photon detection efficiency (PDE) and GAPD2 with 100 × 100 µm2 of 45% PDE. The number of counted photons in each photosensor was analytically calculated. The LCE, linearity and flood histogram were examined for each PET detector module having 99 different configurations as a function of light guide thickness ranging from 0 to 10 mm. ResultsThe performance of PET detector modules based on GAPDs was considerably improved by using the thick light guide. The LCE was increased from 24 to 30% and from 14 to 41%, and the linearity was also improved from 0.97 to 0.99 and from 0.75 to 0.99, for GAPD1 and GAPD2, respectively. As expected, the performance of PSPMT based detector did not change. The flood histogram of 12 × 12 array PET detector modules using 3 mm light guide coupled with GAPDs was obtained by simulation, and all crystals of 1 × 1 × 20 mm3 size were clearly identified. PET detector module coupled with thick light guide and GAPD array with large-area microcells was proposed to obtain high QE and high spatial resolution, and its feasibility was verified. ConclusionsThis study demonstrated that the overall PET performance of the proposed design was considerably improved, and this approach will provide opportunities to develop GAPD based PET detector with a high LCE.