Avalanche Photodiodes Research Articles

Multichannel FPGA-based Data Acquisition System for Fan-beam Dual Energy X-ray Absorptiometry

This study aimed to develop a multichannel field programmable gate array (FPGA) based data acquisition (DAQ) system that could process 8 analog signals from a 1 × 8 LYSO array coupled with a Geiger-mode avalanche photodiode (GAPD) for fan-beam dual-energy X-ray absorptiometry (DEXA) system. Each analog input signal was digitized using an 8-channel analog-to-digital converter (ADC) with a 125 MHz sampling rate and an input range of -1.0 to 1.0 V. The 14-bit digital signals were then fed into a Xilinx Virtex-6 FPGA-based evaluation board that implemented digital signal processing logic. The collected low- and high-energy events of each pixel for each input channel were stored in an on-chip block ram-based first-in-first-out (FIFO) module, and then further transmitted to a personal computer (PC) via the USB port. The intrinsic characteristics, spectral responses, and image acquisition were performed. The estimated coefficient of determination (R²) was 0.999 in voltage linearity and no considerable alterations in voltage resolution were observed. The energy resolutions of the peak 59.5 keV (Am-241) were ~28.2 %. Dual-energy peaks were isolated in the X-ray energy spectra. The synchronization between the movement part of the DEXA system and the timing control block inside the FPGA chip was well controlled in various conditions. The DEXA phantom images for each pixel were clearly resolved. This study demonstrated that FPGA with only on-chip memory resources can be used to build a multichannel DAQ system for fan-beam DEXA systems.

Design and Optimization of High-Responsivity High-Speed Ge/Si Avalanche Photodiode in the C+L Band.

We present the design of Ge/Si avalanche photodetectors with SiN stressor-induced Ge strain for the C+L band light detection. By optimizing the placement position and thickness of the SiN layer with compressive stress, a uniform strain distribution with a maximum magnitude of 0.59% was achieved in Ge. The surface-illuminated APDs have been studied in respect of the photo-dark current, responsivity, gain, and 3-dB bandwidth. After introducing SiN stressor, the APD exhibits high primary responsivity of 0.80 A/W at 1.55 μm, 0.72 A/W at 1.625 μm, and 3-dB bandwidth of 17.5 GHz. The increased tensile strain in Ge can significantly improve the responsivity and broaden the response band of the device. This work provides a constructive approach to realizing high-responsivity high-speed Ge/Si APD working in the C+L band.

Improved performance of AlGaN solar-blind avalanche photodiodes with dual multiplication layers

Improved performance of AlGaN solar-blind avalanche photodiodes with dual multiplication layers

Resolution of 100 photons and quantum generation of unbiased random numbers

Macroscopic quantum phenomena, such as observed in superfluids and superconductors, have led to promising technological advancements and some of the most important tests of fundamental physics. At present, quantum detection of light is mostly relegated to the microscale, where avalanche photodiodes are very sensitive to distinguishing single-photon events from vacuum but cannot differentiate between larger photon-number events. Beyond this, the ability to perform measurements to resolve photon numbers is highly desirable for a variety of quantum information applications, including computation, sensing and cryptography. True photon-number resolving detectors do exist, but they are currently limited to the ability to resolve on the order of 10 photons, which is too small for several quantum-state generation methods based on heralded detection. Here we extend photon measurement into the mesoscopic regime by implementing a detection scheme based on multiplexing highly quantum-efficient transition-edge sensors to accurately resolve photon numbers between 0 and 100. We then demonstrate the use of our system by implementing a quantum random-number generator with no inherent bias. This method is based on sampling a coherent state in the photon-number basis and is robust against environmental noise, phase and amplitude fluctuations in the laser, loss and detector inefficiency as well as eavesdropping. Beyond true random-number generation, our detection scheme serves as a means to implement quantum measurement and engineering techniques valuable for photonic quantum information processing. A spatially multiplexed detection system of three transition-edge sensors is developed to resolve photon numbers up to 100 in a single laser pulse. Using the detector to measure parity of a coherent state allows for the extraction of quantum random numbers.

Top-Illuminated Avalanche Photodiodes With Cascaded Multiplication Layers for High-Speed and Wide Dynamic Range Performance

In this work, a novel top-illuminated avalanche photodiode (APD) with a In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As multiplication (M-) layer is demonstrated. The cascaded M-layer design combined with the unique p-side up mesa structure allows relaxation of the fundamental trade-off between the gain-bandwidth product and the dark current. This leads to the simultaneous high-responsivity, high-speed, high-saturation-power, and low-dark current characteristics of our APDs. At around 0.9 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> operation, the demonstrated device with its simple top-illuminated structure and large active window (mesa) diameter of 14 (24) μm exhibits a high responsivity (2.23 A/W), wide optical-to-electrical bandwidth (30 GHz), large gain-bandwidth product (270 GHz), low dark current (∼200 nA), and a saturation current as high as 11 mA. The excellent performance of this APD structure opens up new possibilities to further enhance the sensitivity performance of receivers for coherent communications or 106 Gbit/sec PAM-4 applications.

The performance of millimeter-wave over fiber using electro absorption modulator and avalenche photodiode

In this paper, a parallel MZM and a quadrupling frequency technique are used to produce a 72 GHz mm-wave. The determined optical sideband suppression ratio (OSSR) is 71 decibels. This mm-wave signal's performance is compared to that of two optical modulators, the Mach Zehnder Modulator (MZM) and the Electro Absorption Modulator (EAM) as well as two different kinds of photodiodes, the Avalanche Photodiode (APD) and the PIN-PD. When using the EAM modulator, the maximum Q factor for 80 km is almost 20, but when using MZM, it is only 2.3. The performance of the generated mm-wave was then investigated using two different types of PD, PIN and APD, as optical receivers to achieve the best result in terms of signal quality. When compared to PIN-PD, APD improves the power of the received 72 GHz signal by 35%. The system's ability to carry a higher data rate is tested by successfully varying the bit rate up to 10 Gb/s over a distance of 20 km.

Development of Time- and Energy-Resolved Synchrotron-Radiation-Based Mössbauer Spectroscopy

Synchrotron-radiation based Mössbauer spectroscopy has become a useful technique capable for investigating various Mössbauer isotopes. For a typical experimental setup, the information associated with the pulse height (that is, energy) in an avalanche photodiode (APD) detector has not been used effectively. By using a system for simultaneous measurement system of time and energy associated with the APD signal, a system for the time- and energy-resolved Mössbauer spectroscopy has been developed. In this system, the pulse height information was converted to the time information through an amplitude-to-time converter applied to one of the divided signals from the APD. The corresponding time information was processed separately from another one of the divided signals. Both signals are recorded by a multi-channel scaler in an event-by-event data acquisition process. The velocity information from the Mössbauer transducer was also recorded as a tag for each signal event. Thus, the Mössbauer spectra with any time- and energy-window can be reconstructed after the data collection process. This system can be used for many purposes in time- and energy-resolved Mössbauer spectroscopy, and shows significant promise for use with other fast detectors and for various types of experiments.

Optical Detection Method for Partial Discharge of Printed Circuit Boards in Electrified Aircraft Under Various Pressures and Voltages

Realization of an electrical aircraft demands a low-weight electric distribution and propulsion system. The use of high voltage and power electronics operated at high switching frequencies is essential to achieve this objective. However, printed circuit boards (PCBs) in electrified aircraft are in a harsh working environment, which can make PCBs more susceptible to generate partial discharges (PDs). The current PD detection technology has poor immunity to the electromagnetic interference and acoustic interference in the operating environment of aircraft. Therefore, this article proposes an optical-based PD detection method for PCBs, which is effectively immune to electromagnetic and acoustic interference. This method uses fluorescent fiber as a PD optical signal sensor and then collects the optical signal by the avalanche photodiode (APD). Experiments have verified that the detection sensitivity, sensing range, and anti-interference performance of this method are well satisfied with the PD detection. In addition, single PD pulse, optical phase resolved PD (PRPD) patterns, and PD inception voltage (PDIV) under different air pressure and voltage conditions are investigated. Finally, the relationship between the optical signal and PD amplitude is found to be proportional, which proves that the severity of the PD on PCBs can be effectively detected and evaluated by this method.

Photodiode-body-biased MOSFET with adjustable gain from 1 to 106 and wide dynamic range over 160 dB, enabling optical measurement applications

Optical sensors have been found in numerous measurement applications for scientific instrumentation and spectrometers. To achieve a high gain, devices such as photomultiplier tubes (PMTs), avalanche photodiodes (APDs), and phototransistors are commonly used. PMTs with high gain of >105 are bulky and have high power consumption. Compact APDs tend to have high shot noise and strong temperature dependence. Phototransistors taking advantage of current amplification of bipolar junction transistors (BJTs), on the other hand, do not require high electric field to attain a gain of 10–100. Here, this work addresses a new optical sensor design with an adjustable gain from 1 to 106 and a wide dynamic range over 160 dB. The sensor is based on light-modulated body-bias effect and can be manufactured by commercial CMOS technology.

Study of gain, noise, and collection efficiency of GaAs SAM-APDs single pixel

III-V-compound semiconductors offer many advantages over silicon-based technologies traditionally used in solid-state photodetectors, especially in hard X-ray applications that require high detection efficiency and short response times. Amongst them, gallium arsenide (GaAs) has very promising characteristics in terms of X-ray absorption and high carrier velocity. Furthermore, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics. This work reports on the experimental characterization by means of lasers and synchrotron radiation of gain, noise, and charge collection efficiencies of GaAs avalanche photodiodes (APDs), realized by molecular beam epitaxy (MBE), featuring separate absorption and multiplication regions (SAM) and different absorption region thicknesses. These devices have been fabricated to investigate the role of the thickness of the absorption region and of possible traps or defects at the metal-semiconductor interfaces in the collection efficiency in order to lay the groundwork for the future development of thicker GaAs devices for detection of hard X-rays.

Double-Pulse Superposition Technique for Avalanche Extraction From Gated InGaAs/InP Single-Photon Detectors

Gated InGaAs avalanche photodiodes are often used for synchronous single-photon detection in the near-infrared wavelengths of 1310 and 1550 nm for optical fiber communication. However, one of the main obstacles limiting their application is the difficulty in extracting a weak photon-induced avalanche pulse from background noise. Here, we describe a double-pulse superposition technique to detect the signal, which uses a synchronized pulse to raise the avalanche signal above the discriminating threshold so the avalanche signal can be easily detected. This technique provides a simple idea for a practical gated single-photon detector to sense avalanche signals since the parasitic capacitance signal from an applied external circuit is unavoidable and will always be coupled to the avalanche signal. Under the same measurement conditions, a comparison was made with the conventional capacitive balance technique, and the experimental results showed a high agreement between the effects of the two signal extraction techniques under several nanoseconds scale gating widths, and the double-pulse superposition technique is highly efficient and easy to implement even under complicated background noise.

Gas puff imaging on the TCV tokamak.

We present the design and operation of a suite of Gas Puff Imaging (GPI) diagnostic systems installed on the Tokamak à Configuration Variable (TCV) for the study of turbulence in the plasma edge and Scrape-Off-Layer (SOL). These systems provide the unique ability to simultaneously collect poloidal 2D images of plasma dynamics at the outboard midplane, around the X-point, in both the High-Field Side (HFS) and Low-Field Side (LFS) SOL, and in the divertor region. We describe and characterize an innovative control system for deuterium and helium gas injection, which is becoming the default standard for the other gas injections at TCV. Extensive pre-design studies and the different detection systems are presented, including an array of avalanche photodiodes and a high-speed CMOS camera. First results with spatial and time resolutions of up to ≈2 mm and 0.5µs, respectively, are described, and future upgrades of the GPI diagnostics for TCV are discussed.

Eye-safe photon counting LIDAR for magmatic aerosol detection

An eye-safe photon counting light detection and ranging (LIDAR) instrument has been developed for magmatic aerosol sensing in real time. The developed LIDAR was based on a pulsed diode laser (transmitter, 910 nm, 3 ns, <1 µJ cm−2) and a single-photon avalanche photodiode. The instrument was designed to fit the requirements of highly sensitive sensing of aerosol dynamics at distances up to 50 meters. The accuracy of the LIDAR instrument ranging was estimated as 18 cm. Field experiments inside the Baksan Neutrino Observatory tunnel above the volcano Elbrus chamber revealed a good correlation between the magmatic aerosol dynamics and the Earth’s crust deformation due to Moon and Sun tides quantified by a tiltmeter and a laser strainmeter.

Efficient Avalanche Photodiodes with a WSe2/MoS2 Heterostructure via Two-Photon Absorption.

Two-dimensional (2D) materials-based photodetectors in the infrared range hold the key to enabling a wide range of optoelectronics applications including infrared imaging and optical communications. While there exist 2D materials with a narrow bandgap sensitive to infrared photons, a two-photon absorption (TPA) process can also enable infrared photodetection in well-established 2D materials with large bandgaps such as WSe2 and MoS2. However, most of the TPA photodetectors suffer from low responsivity, preventing this method from being widely adopted for infrared photodetection. Herein, we experimentally demonstrate 2D materials-based TPA avalanche photodiodes achieving an ultrahigh responsivity. The WSe2/MoS2 heterostructure absorbs infrared photons with an energy smaller than the material bandgaps via a low-efficiency TPA process. The significant avalanche effect with a gain of ∼1300 improves the responsivity, resulting in the record-high responsivity of 88 μA/W. We believe that this work paves the way toward building practical and high-efficiency 2D materials-based infrared photodetectors.

Scanning-based photon-limited imaging through scattering media

Imaging through scattering media has attracted considerable research interest in recent years. Most existing studies are dedicated to reconstructing objects from the detected speckle pattern in an array-based system. However, the inevitable aliasing effect among pixels degrades the imaging quality significantly. Therefore, most existing studies usually could only work well under a weak scattering medium and a short working distance. To address this issue, we innovatively propose a robust scanning-based photon-limited imaging system for imaging through scattering media. To boost the imaging capability, we specifically adopt a point-to-point scanning strategy to eliminate the aliasing effect, and utilize a Geiger-mode avalanche photo diode to detect extremely weak signals after passing through the scattering media. As the images captured by the proposed imaging system always suffer from Poisson noise at unknown levels, we further construct a blind deep-learning based denoising framework with “one-to-all” strategy. By introducing a noise estimation sub-network with dense connection and batch normalization operations into the whole denoising framework, one trained model with synthetic datasets based on the realistic noise model could be generalized well to all real captured photon-limited images. Extensive experiments in real situations demonstrate that significant improvements can be achieved in the proposed method. For example, clear objects can be observed through several thick scattering media under an approximate working distance of 7 m, even with a low-power (average power of approximately 20 mW) light source.

The front-end electronics upgrade of the CMS ECAL barrel

The barrel part of the CMS electromagnetic calorimeter (ECAL) consists of 61200 PbWO4 crystals coupled to avalanche photodiodes (APDs). A decrease of the ECAL operating temperature from 18 °C to 9 °C is needed to mitigate the increase in APD noise from radiation-induced dark current in the conditions of the high luminosity upgrade of the LHC. Moreover, a full re-design of the front-end electronics has been undertaken in order to deal with the increase of pileup events and to improve the rejection of anomalous signals generated from direct interaction with the APDs. The VFE (Very Front-End) card will be equipped with two new ASICs: a fast trans-impedance amplifier named CATIA as well as a data conversion and compression ASIC named LiTE-DTU. The VFE will interface with the radiation tolerant LpGBT transceiver and the VTRx+ optical board, while trigger primitive generation will be moved off-detector to FPGA-based processors. The CATIA ASIC has a single input and two differential outputs with different gains in order to have better resolution for low energy signals. CATIA is designed in commercial CMOS 130 nm technology and can be controlled via an I2C interface. The LiTE-DTU ASIC embeds two 12-bit 160 MS/s ADCs, a sample selection logic, a lossless compression digital logic, and a 1.28 Gb/s serializer that will directly interface with the LpGBT e-links. LiTE-DTU is designed in commercial CMOS 65 nm technology. It embeds a PLL for the generation of the low jitter 1.28 GHz clock required by the ADCs and the serializer. Both ASICs have been extensively tested in lab and beam tests. This new system has been verified to fulfill the requirements of the experiment in terms of performance and radiation tolerance. The ASICs are now in the pre-production phase.

InGaAsP/InP Geiger-Mode Avalanche Photodiode Towards Sub-kHz Dark Count Rate at 20% Photon Detection Efficiency

Geiger-mode InGaAsP/InP single photon avalanche photodiode (SPAD) with a low dark count rate (DCR) of 870 Hz at a photon detection efficiency (PDE) of 20% at 1064 nm is achieved for a 40 micron diameter device at −30 °C. Extensively optimized and accurately controlled shallow/deep two-step pn junction and doping profiles are identified to play decisive roles for the performance improvement. While a state-of-the-art specific detectivity of 1.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W is realized for the optimized SPAD, a temperature coefficient of the breakdown voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> ) of 139 mV/K, a dark current of 200 pA at 90%V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> and a timing jitter of 280 ps at 20% PDE are also simultaneously attained. Thermal activation energies of approximate 0.5 eV are observed for both the dark current and the DCR at 253–293 K, indicates the dominant source of dark carriers is the mid-gap defect trapping states-related tunneling in the InGaAsP absorber.

Performance evaluation of high-dimensional quantum key distribution with single-photon detector based on avalanche photodiode

The current theoretical analysis model for high-dimensional quantum key distribution (QKD) was developed without carefully considering the dead time and after-pulse of the single-photon detectors. Here, we propose a new model that accounts for these two effects. With this model, we analyze the effects of various properties of the single-photon detector on the performance of the high-dimensional quantum key distribution and show numerically that the high-dimensional quantum key distribution can be achieved up to 180 km with InGaAs/InP-type single-photon detectors. This work can improve our understanding of the factors that determine the performance of high-dimensional quantum key distribution and will help to promote the application of single-photon detectors based on avalanche photodiodes in high-dimensional quantum key distribution.

A very low-cost pulse-amplitude modulated chlorophyll fluorometer

The quantum yield of photosystem II (ϕPSII) is an important metric to determine a plant’s light use efficiency and to detect plant stresses. Commercial instruments that measure ϕPSII exist, but their cost may prevent widespread adoption. We present the design and realization of a chlorophyll fluorometer capable of measuring ϕPSII that uses a minimal set of optical components and relies on low-cost electronics with total component costs below USD 300. A consumer grade 405 nm laser diode obviates the need for optical elements in the excitation path, and an avalanche photodiode ensures high sensitivity. In addition, an emission filter and a collimating lens are needed. We demonstrate sensor linearity and actinic light immunity with fluorescence reference standards, and we compare our device to a commercial instrument to assess accuracy: With three plant species (Spathiphyllum, Heuchera, and Hosta) and under actinic light variations from zero to 450 μmolm−2s−1, reported ϕPSII from both instruments correlated with R2=0.87. Implications of our design choices, their costs, and alternatives are discussed.

ОЦЕНКА ВЛИЯНИЯ ФУНКЦИОНАЛЬНЫХ ЭЛЕМЕНТОВ НА ПАРАМЕТРЫ СИСТЕМЫ КВАНТОВОГО РАСПРЕДЕЛЕНИЯ КЛЮЧА НА ОСНОВЕ ПРОТОКОЛА B92

The influence of the parameters of functional elements on the energy, time and probabilisticcharacteristics of the quantum key distribution system (QKD) based on the B92 protocol is studied.The dependences of the probability of writing correct and erroneous bits into a raw quantumkey sequence are plotted for various lengths of a fiber-optic communication line (FOCL) and theuse of various lasers (EML-laser; DFB-laser; VCSEL-laser and FP-laser) and photodetectormodules (id201; id210; id220; id230). Thus, changes in the probability of writing a correct bit intoa raw quantum key sequence are much more significant than changes in the probability of writingan erroneous bit (50.9 times versus 3.3 times with FWHM=80 pm and a change in the length ofthe FOCL from 10 to 100 km). This is due to the fact that with an increase in the length of theFOCL, the probability of the absence of registration at the receiving station of photons or darkcurrent pulses (DCP) sharply increases. Numerical material indicates a direct proportional dependenceof the probability of writing an erroneous bit on the frequency of generation of noisepulses of single-photon avalanche photodiodes (SAPD). So, with an increase in the frequency ofoccurrence of DCP by 60 times (from 100 to 6000 Hz), the probability of recording an erroneousbit also increases by 60 times (for example, with a FOCL length of 100 km – 6.39 versus 383.3).It has been established that the root-mean-square deviation of the photon delay time is directly proportional to the length of the FOCL and the width of the laser spectrum. With a spectrum widthof FWHM=10 pm and an increase in the FOCL length from 10 to 100 km (by a factor of 10), thestandard deviation of the photon delay time also increases by a factor of 10 (from 4.16 to 41.6 ps).To achieve the best performance of the QKD system as a whole, it is advisable to use a laser witha minimum width of the radiation spectrum, for example, an EML-laser. However, EML-lasers areconsidered the most complex and expensive of all the considered types of lasers, so the use ofEML-lasers significantly increases the cost of the entire QKD system.