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In this paper we present a new technology for the fabrication of Single Photon Avalanche Diodes (SPADs) aimed at combining the advantages of thin and thick SPADs. The new detector is manufactured in a thick epitaxial layer designed to improve the Photon Detection Efficiency (PDE) in the red and near-infrared range while maintaining a good timing resolution. Experimental characterization of the new red-enhanced SPAD (RE-SPAD) confirmed a significant improvement of the PDE compared with thin SPADs; for example the PDE at a wavelength of 800 nm has increased from 15% to about 40%. Nevertheless the temporal resolution is still good, with a timing jitter of about 90 ps FWHM. In the same operating conditions the dark count rate is comparable with the one attainable with a thin SPAD (e.g. less than 25 cps for a 50 µm diameter device cooled down to −5°C). Moreover, being planar, the new technology is compatible with the fabrication of arrays of detectors. [ABSTRACT FROM PUBLISHER]

Multi-dimensional time correlated single-photon counting has reached a prominent position among analytical techniques employed in the medical and biological fields. The development of instruments able to perform temporal and spectral fluorescence analysis (sFLIM) at the same time is limited by the performance of single-photon detectors, since currently available arrays cannot simultaneously satisfy all the requirements. To face this rising quest, a fully-parallel eight-channel module, based on a monolithic single-photon avalanche diode (SPAD) array with great temporal resolution, high photon detection efficiency and low dark count rate, has been designed and fabricated. The system relies on a novel architecture of the single pixel, based on the integration of the timing pick-up circuit next to the photodetector, making the negative effects of electrical and optical crosstalk on photon timing performance negligible. To this end, the custom technological process used to fabricate the SPAD has been modified, allowing the integration of MOS transistors without impairing the structure and the performance of the detector. The single channel is complemented by an external active quenching circuit, fabricated in a standard CMOS technology, that ensures high maximum counting rate (>5 MHz) and low after-pulsing (<2%). Finally, the output timing signals are read and conditioned by proper CMOS electronics. The complete system shows a very good temporal resolution of about 45 ps (FWHM). [ABSTRACT FROM AUTHOR]

After a brief review of the physics of photon detection in single photon avalanche diode (SPAD) devices, in this paper we will outline the principle of operation of a model we developed with the aim of calculating both photon detection efficiency (PDE) and temporal response (TR) of these detectors. Then we will apply the model to the devices currently available in order to critically analyze some experimental results. We will show in particular how the use of the model allows us to gain a better understanding of the influence of each device parameter in determining both the PDE and the TR. Finally we will discuss some modifications that can be applied to the device structure in order to overcome such limitations. Their effectiveness in improving both the PDE and the TR will be investigated by means of the aforementioned model. The aim is to provide the reader with an insight of which performances can be expected in the next few years if a strong development of the SPAD structure is pursued. [ABSTRACT FROM AUTHOR]

Recent advances in fluorescence measurements for single molecule spectroscopy, genomics, proteomics and medical diagnostics require single-photon detectors with high quantum efficiency in the extended red spectral range (from 600 nm to 900 nm) and low noise (<50 kc s-1). Amongst industrial production, avalanche photodiodes with large diameter (up to 500 µm) are available which can work in Geiger mode (GM) with good photon detection efficiency (higher than 20%) and some of them also with quite low dark counting rate. They allow one to attain high collection efficiency with simple optical systems. However, they work at high bias voltage (over 200 V) with high power dissipation and are easily damaged by exposure to intense light. A detector carrier module has been designed for safe operation and full performance exploitation of any silicon device suitable for GM operation, with any breakdown voltage up to 480 V. Efficient photon counting and timing is achieved in a very compact module by means of an integrated active-quenching circuit (iAQC) with fast time pickup. Catastrophic failure is avoided by a dedicated monitor and safety circuit, even in the case of exposure to sunlight. [ABSTRACT FROM AUTHOR]

The evolution of solid-state avalanche detectors of single optical photons is outlined and the issues for further progress are discussed. Physical phenomena that underlay the operation of the single-photon avalanche diodes (SPAD) and determine the performance are considered and their role is assessed (detection efficiency; dark-counting rate; afterpulsing; photon timing resolution; etc.). The main technological issues that hamper the development of detectors with wide sensitive area and of array detectors with high filling factor are illustrated. Silicon SPADs are the main focus of attention; infrared-sensitive SPADs in germanium and in compound semiconductors are also dealt with. The role of the active-quenching circuits (AQC) is assessed and the evolution is outlined up to integrated AQCs, which offer the prospect of monolithic integration of complete photon counter instruments. [ABSTRACT FROM AUTHOR]

New detector modules exploit recent progress in the technology of silicon single-photon avalanche diodes (SPADs) and in the design of associated electronic circuits. SPAD detectors with diameter up to 100 µm, good photon detection efficiency (48% peak at 550 nm wavelength) and low dark counting rate are used in these modules. Monolithic integrated active-quenching circuits (iAQC) and fast time-pickoff circuits ensure efficient photon counting and timing, with better than 50 ps FWHM time resolution and less than 50 ps centroid shift for counting rates up to 4 Mc/s. Experimental tests of the module performance and an application example are presented. [ABSTRACT FROM AUTHOR]

Polymers carrying different reactive groups that can be orthogonally functionalized are desirable for the design of multi-functionalizable materials. While several orthogonally functionalizable polymers have been reported, most of the work utilizes handles that are reactive toward different functional groups. However, examples of polymers that are orthogonally reactive toward molecules bearing the same functional group are rare. In this work, we report polymeric materials that can be sequentially functionalized using different amine-bearing molecules. Herein, we synthesized isocyanate and epoxide group containing copolymers, and investigated their sequential functionalization with amine-containing molecules. We show that such copolymers can be first functionalized with a particular amine-bearing molecule at room temperature, using conjugation through the isocyanate group. Thereafter, a different amine-containing molecule can be attached through the epoxy-amine reaction at 65 °C. Chemical characterizations of parent and subsequently functionalized copolymers were done by 1H NMR and FTIR spectroscopy techniques, to establish orthogonal functionalization. Additionally, the epoxide side chains were utilized as surface anchoring group after the functionalization of the polymer via isocyanate-amine reaction. This straightforward approach for obtaining orthogonally reactive amine-functionalizable copolymers, and surfaces derived thereof, would be attractive materials for various biomedical applications. [ABSTRACT FROM AUTHOR]

This paper intends a Euler-Lagrange passivity-based controller (EL-PBC) for the three-level (TL) Ćuk PFC converter for EVs battery charging application. The TL Ćuk converter has features of reduced filter size and voltage stress of switches. First, the Euler-Lagrange formulation is used to develop the mathematical modelling. Then, the EL-PBC methodology is implemented by injecting a virtual resistor in series with the input inductor. Further, the stability analysis is also carried out. To improve the performances against input perturbations and reduce the steady state error, a PI controller is integrated with the aforesaid controller and its performances are investigated. Furthermore, the power quality of the charger is assessed and it satisfies IEC 61000-3-2 Class C standard. This controller is also compared with the benchmark PI controller. A prototype model of same specifications is tested in hardware in loop. Computer simulations and test results are presented to validate the theoretical aspects. [ABSTRACT FROM AUTHOR]

Over the past few years there has been a growing interest in monolithic arrays of single photon avalanche diodes (SPADs) for parallel detection of faint ultrafast optical signals. SPADs implemented in CMOS-compatible planar technologies offer the typical advantages of microelectronic devices (small size, ruggedness, low voltage, low power, etc.). Furthermore, they have inherently higher photon detection efficiency than photomultiplier tubes and they are able to provide very high acquisition speeds. The development of fully-parallel multichannel systems is a challenge both for the detector (with new problems like optical and electrical crosstalk, isolation elements size reduction and the need for higher yields) and for the electronics. The development of a parallel detector must be accompanied by that of the time-to-amplitude converters and analysis electronics necessary in time-correlated single photon counting applications. In this paper we present the fundamental building blocks necessary to develop a parallel picosecond array detector: a new high-performance SPAD detector, compatible with the design of multi-detector systems with a large number of channels, and a new totally integrated system for time-to-amplitude conversion, to allow the simple integration of several channels on a single chip. [ABSTRACT FROM AUTHOR]

This work proposes a compact time-to-amplitude converter (TAC) for single-photon time-of-flight (TOF) measurement. Based on the principle of current mirror integration, the regulated cascode output structure is used to improve the integration linearity. Fabricated in 180 nm standard CMOS technology, the test results show that the proposed TAC achieves an integral nonlinearity of less than 1.1 LSB, and a timing resolution of 78 ps in a full-scale range (FSR) of 20 ns. Moreover, the readout voltage only varies by 1% during 1 ms hold-off time. The simple circuit structure make TAC occupy a small area of 120 µm2 and consume low dynamic power of 36.8 µW. The TOF measurement error is less than 5.2 cm, and the measurement precision is up to 1.61 cm at 150 cm. The presented TAC provides a compact implementation solution to realize high-density TOF sensors. [ABSTRACT FROM AUTHOR]

We have performed a statistical characterization of the effect of afterpulsing in a free-running silicon single-photon detector by measuring the distribution of afterpulse waiting times in response to pulsed illumination and fitting it by a sum of exponentials. We show that a high degree of goodness of fit can be obtained for five exponentials, but the physical meaning of estimated characteristic times is dubious. We show that a continuous limit of the sum of exponentials with a uniform density between the limiting times gives excellent fitting results in the full range of the detector response function. This means that in certain detectors, the afterpulsing is caused by a continuous band of deep levels in the active area of the photodetector. [ABSTRACT FROM AUTHOR]

The main purpose for this work is to study the challenges of designing a digital buck regulator using pipelined analog to digital converter (ADC). Although pipelined ADC can achieve high sampling speed, it will introduce additional phase lag to the buck circuit. Along with the latency brought by processing time of additional digital circuits, as well as the time delay associated with the switching frequency, the closed loop will be unstable; moreover, raw ADC outputs have low signal-to-noise ratio, which usually need back-end calibration. In order to compensate these phase lag and make control loop unconditional stable, as well as boost up signal-to-noise ratio of the ADC block with cost-efficient design, a finite impulse response filter followed by digital proportional-integral-derivative blocks were designed. All these digital function blocks were optimised with processing speed. In the system simulation, it can be found that this controller achieved output regulation within 10% of nominal 5 V output voltage under 1 A/µs load transient condition; moreover, with the soft-start method, there is no turn-on overshooting. The die size of this controller is controlled within 3 mm2by using 180 nm CMOS technology. [ABSTRACT FROM PUBLISHER]

Silicon photomultipliers (SiPMs) are large area detectors consisting of an array of single-photon-sensitive microcells, which make SiPMs extremely attractive to substitute the photomultiplier tubes in many applications. We present the design, fabrication, and characterization of analog SiPMs in standard planar 0.35 μm CMOS technology, with about 1 mm × 1 mm total area and different kinds of microcells, based on single-photon avalanche diodes with 30 μm diameter reaching 21.0% fill-factor (FF), 50 μm diameter (FF = 58.3%) or 50 μm square active area with rounded corner of 5 μm radius (FF = 73.7%). We also developed the electrical SPICE model for CMOS SiPMs. Our CMOS SiPMs have 25 V breakdown voltage, in line with most commercial SiPMs and higher gain (8.8 × 106, 13.2 × 106, and 15.0 × 106, respectively). Although dark count rate density is slightly higher than state-of-the-art analog SiPMs, the proposed standard CMOS processing opens the feasibility of integration with active electronics, for switching hot pixels off, drastically reducing the overall dark count rate, or for further on-chip processing. [ABSTRACT FROM PUBLISHER]

Plasma in low earth orbit can damage electronic components and potentially jeopardize scientific missions in space. Predicting the accumulated damage and understanding components’ radiation tolerance are important in mission planning. In this manuscript, we report on the observed radiation tolerance of single photon detectors and a liquid crystal polarization rotator. We conclude that an uncooled Si APD could continue to operate from more than a month up to beyond the lifetime of the satellite depending on the orbit. The liquid crystal polarization rotator was also unaffected by the exposed dosage. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Because its original use as a treatment for hematologic disease, more recently immunotherapy has emerged as a novel effective therapeutic strategy for solid malignancies, such as melanoma and prostate carcinoma. For breast carcinoma, an immunologic therapeutic approach has not been well evaluated, even though there is evidence to suggest it would be a successful novel strategy, especially taking into account the high mortality rate of the most aggressive variants of this heterogeneous disease. Here, we briefly describe the most recently awarded immune-based therapies with a consolidated or potential implication for the treatment of solid malignancies. We focus on immune checkpoints and on the clinical potential of their abrogation, with a further overview of novel vaccine-based approaches and the most relevant immunotherapeutic techniques. We aim to provide an exhaustive review of the most promising immune-therapeutic agents that may have implications for breast cancer treatment. [ABSTRACT FROM AUTHOR]

Many demanding applications require single-photon detectors with very large active area, very low noise, high detection efficiency, and precise time response. Single-photon avalanche diodes (SPADs) provide all the advantages of solid-state devices, but in many applications other single-photon detectors, like photomultiplier tubes, have been preferred so far due to their larger active area. We developed silicon SPADs with active area diameters as large as 500 μm in a fully standard CMOS process. The 500 μm SPAD exhibits 55% peak photon detection efficiency at 420 nm, 8 kcps of dark counting rate at 0°C, and high uniformity of the sensitivity in the active area. These devices can be used with on-chip integrated quenching circuitry, which reduces the afterpulsing probability, or with external circuits to achieve even better photon-timing performances, as good as 92 ps FWHM for a 100 μm diameter SPAD. Owing to the state-of-the-art performance, not only compared to CMOS SPADs but also SPADs developed in custom technologies, very high uniformity and low crosstalk probability, these CMOS SPADs can be successfully employed in detector arrays and single-chip imagers for single-photon counting and timing applications. [ABSTRACT FROM PUBLISHER]

To assess PAH contamination state of Monastir Bay, surface sediments were collected and analysed for 17 selected parent PAHs by GC/MS. Sediments were sampled from five sites in wet and dry seasons. Total PAH concentrations were in the range of 25.6 to 576.8 ng/g d.wt in winter and 44.9–395.8 ng/g d.wt in summer. Comparison of results with Sediment Quality Guidelines suggested no eco-toxicological risk for benthic organisms. The use of molecular indices has shown that PAHs in surface sediments originate mainly from pyrolytic sources. Total PAH concentrations in surface sediments showed no significant correlations with organic matter content and pelite fraction. The analysis of spatial and seasonal variations of PAHs in surface sediments has demonstrated that final distribution of PAHs in surface sediments is mainly governed by hydrological conditions. [ABSTRACT FROM AUTHOR]

Modern time-correlated single-photon counting (TCSPC) systems can achieve very high performance, but advanced applications also demand the implementation of multichannel acquisition chains. To fit the specifics of TCSPC applications we developed a complete single-channel measurement system, composed by three main parts: a single-photon detection module, a TCSPC acquisition board and a power management unit. The system is based on a single-photon avalanche diode (SPAD) and on a fully integrated time-to-amplitude converter (TAC). We designed the module to be very compact, in order to be enclosed in a small case (110 × 50 × 40 mm). The system features high temporal resolution (71 ps), low differential nonlinearity (0.05 LSB), high counting rate (4 MHz) and low power. Moreover a four-channel TAC has already been manufactured and tested; the very low crosstalk between channels, together with low power and low area make the converter suitable for large scale multi-channel acquisition chains, allowing the implementation of architectures for multidimensional TCSPC measurements. [ABSTRACT FROM PUBLISHER]

The characterization and analysis of afterpulsing behavior in InGaAs/InP single photon avalanche diodes (SPADs) is reported for gating frequencies between 10 and 50 MHz. Gating in this frequency range was accomplished using a matched delay line technique to achieve parasitic transient cancellation, and FPGA-based data acquisition firmware was implemented to provide an efficient, flexible multiple-gate sequencing methodology for obtaining the dependence of afterpulse probability P ap on hold-off time T ho. We show that the detrapping times extracted from the canonical exponential fitting of P ap(T ho) have no physical significance, and we propose an alternative description of the measured data, which is accurately fit with the simple power law behavior P ap ∝  with α ∼ 1.2 ± 0.2. We discuss the physical implications of this functional form, including what it may indicate about trap defect distributions and other possible origins of this power law behavior. [ABSTRACT FROM PUBLISHER]

InGaAs/InP-based semiconductor avalanche photodiodes are usually employed for single-photon counting at telecom wavelength. However they are affected by afterpulsing which limits the diode performance. Recently, Princeton Lightwave has commercialized a diode integrating monolithically a feedback resistor. This solution effectively quenches the avalanche and drastically reduces afterpulsing. Here, we report the development and characterization of a detector module based on this diode, implementing an active hold-off circuit which further reduces the afterpulsing and notably improves the detector performances. We demonstrate free-running operation with 600 Hz dark count rate at 10% detection efficiency. We also improved the standard double-window technique for the afterpulsing characterization. Our algorithm implemented by a FPGA allows one to put the APD in a well-defined initial condition and to measure the impact of the higher order afterpulses. [ABSTRACT FROM PUBLISHER]

Breast cancer remains one of the leading causes of death among women across the world. The last few decades have seen significant reduction in mortality owing to earlier detection and better adjuvant treatments that were developed based on clinical staging and morphological features. As these treatments have evolved, the heterogeneity of breast cancer poses a new challenge, since there is no standard gold-therapy suitable for all tumors of the mammary gland. Therefore, contemporary management and research efforts are directed toward specific prognostic and predictive molecular signatures that can guide targeted individualized therapy. The goal of ongoing research in this field is to identify specific molecular targets for developing novel therapeutic approaches. These targets can also serve to improve screening of breast cancer. This review focuses on the role of cancer testis antigens (CTAs) in breast carcinogenesis and explores the potential for development of targeted screening and therapeutic approaches. Normally found in the testes, these antigens are highly correlative with cancers of the breast, skin, and ovaries. These implications have been further corroborated through uncovering the interaction of CTAs with genes and proteins involved in tumor suppression and homeostasis like p53. There is some evidence that these genes can be targeted for early detection in addition to being candidates for cancer immunotherapy. [ABSTRACT FROM AUTHOR]

The work focuses on the design and implementation of a field programmable gate array (FPGA) based voltage controller for a single-phase voltage source inverter (VSI) with an inductance-capacitance (L-C) filter. The control algorithm of the open loop and closed loop control schemes of the controller are designed using hardware descriptive languages (VHDL and VerilogHDL) and are implemented using Xilinx SPARTAN 3E FPGA. The sinusoidal pulse-width modulation (SPWM) technique is utilised to realise the controller with a provision to change the modulation index in response with varying load conditions. Suitable L-C filter is designed to minimise the undesirable frequency components in the output voltage. The efficacy of the proposed control schemes in FPGA is validated via successful interface with a prototype VSI and the experimental verification of the controllers are carried out under different loading conditions. [ABSTRACT FROM AUTHOR]

A novel CMOS integrated pulse-width modulation (PWM) control circuit allowing smooth transitions between conversion modes in full-bridge based bi-directional DC-DC converters operating at high switching frequencies is presented. The novel PWM control circuit is able to drive full-bridge based DC-DC converters performing step-down (i.e. buck) and step-up (i.e. boost) voltage conversion in both directions, thus allowing charging and discharging of the batteries in mobile systems. It provides smooth transitions between buck, buck-boost and boost modes. Additionally, the novel PWM control loop circuit uses a symmetrical triangular carrier, which overcomes the necessity of using an output phasing circuit previously required in PWM controllers based on sawtooth oscillators. The novel PWM control also enables to build bi-directional DC-DC converters operating at high switching frequencies (i.e. up to 10 MHz and above). Finally, the proposed PWM control circuit also allows the use of an average lossless inductor-current sensor for sensing the average load current even at very high switching frequencies. In this article, the proposed PWM control circuit is modelled and the integrated CMOS schematic is given. The corresponding theory is analysed and presented in detail. The circuit simulations realised in the Cadence Spectre software with a commercially available 0.18 µm mixed-signal CMOS technology from UMC are shown. The PWM control circuit was implemented in a monolithic integrated bi-directional CMOS DC-DC converter ASIC prototype. The fabricated prototype was tested experimentally and has shown performances in accordance with the theory. [ABSTRACT FROM AUTHOR]

In recent years, time-correlated single-photon counting techniques have been applied to time-of-flight measurements for long-distance range-finding and depth imaging. Depth imaging has been performed by obtaining timing information from an individual single-photon detector and scanning the optical field to obtain a full depth image. Typically, the measurement is made by dwelling on each individual depth pixel for a pre-defined integration time and completing the data acquisition for that pixel before steering the beam to the adjacent spatial position. We present a novel photon-counting data acquisition mode where the time-of-flight histograms for each depth pixel are gradually populated. The system repeatedly scans the same spatial frame with short per-pixel dwell times, and sufficient photon statistics are built up over many frames by cumulating photon events from all acquired frames. The technique is used to compare the depth imaging performance of two single-photon avalanche diode detectors: a novel, resonant-cavity enhanced shallow-junction device; and a commercially available thick-junction device. [ABSTRACT FROM AUTHOR]

An improved gated-mode passive quenching with active reset (gated-PQAR) circuit is utilized in conjunction with an InGaAs/InP single-photon avalanche photodiode (SPAD). Photon detection efficiency (PDE) and dark count probability (DCP) were measured at a gate repetition rate of 1 MHz. The reduced afterpulsing afforded by the gated-PQAR circuit enabled measurement of afterpulsing for hold-off times as short as 10 ns. The timing resolution (jitter) for different excess biases has also been investigated. At 230 K and an excess bias of 2.5 V, 0.3% afterpulse probability for a 10 ns hold-off time was achieved with 13% PDE, 2 × 10-6 DCP, 160 ps jitter, and 0.2 ns effective gate width. For the same hold-off time, at a higher excess bias of 3.5 V, 30% PDE, 1 × 10-5 DCP and 120 ps jitter were achieved with 7% afterpulse probability with an effective gate width of 0.7 ns. [ABSTRACT FROM AUTHOR]

In this Topical Review, we survey the state-of-the-art of single photon detectors based on avalanche diodes fabricated in the InGaAsP materials system for photon counting at near infrared wavelengths in the range from 0.9-1.6 µm. The fundamental trade-off between photon detection efficiency and dark count rate can now be managed with performance that adequately serves many applications, with low dark count rates of ∼1 kHz having been demonstrated at photon detection efficiencies of 20% for 25 µm diameter fiber-coupled devices with thermoelectric cooling. Timing jitter of less than 50 ps has been achieved, although device uniformity is shown to be essential in obtaining good jitter performance. Progress is also reported towards resolving the limitations imposed on photon counting rate by afterpulsing, with at least 50 MHz repetition frequencies demonstrated for 1 ns gated operation with afterpulsing limited to the range of 1-5%. We also present a discussion of future trends and challenges related to these devices organized according to the hierarchy of materials properties, device design concepts, signal processing and electronic circuitry, and multiplexing concepts. Whereas the materials properties of these devices may pose significant challenges for the foreseeable future, there has been considerable progress in device concepts and circuit solutions towards the present imperatives for higher counting rates and simpler device operation. [ABSTRACT FROM AUTHOR]

The state-of-the-art of the NbN nanowire superconducting single-photon detector technology (SSPD) is presented. The SSPDs exhibit excellent performance at 2 K temperature: 30% quantum efficiency from visible to infrared, negligible dark count rate, single-photon sensitivity up to 5.6 µm. The recent achievements in the development of GHz counting rate devices with photon-number resolving capability is presented. [ABSTRACT FROM AUTHOR]

Microchip-based capillary electrophoresis (ME) raises fascinating possibilities for new analytical technologies particularly in the detection of DNA fragments in modern biology. The ME technique has gained considerable popularity with significant progress being made in the development of miniaturized microfluidic devices in micro-volume analysis methods. The ME offers the potential for highly efficient, simultaneous analysis of a large number of biologically important molecules in genomic, proteomic and genetically modified organisms (GMOs) in food stuffs. Recently, the ME technique has greatly impacted biotechnological research with potential applications in smart devices that can operate at the level of molecular manipulation. This review is focused on recent developments and applications of ME to the detection and separation of DNA fragments in various molecules i.e., biotechnological and clinical research. [ABSTRACT FROM AUTHOR]

Geiger-mode avalanche photodiodes (APD) or photon counting detectors (PCD) have become the basis of a range of new detectors and applications. Such devices are sensitive to single photons and are being adapted to create different detector technologies such as the silicon photomultiplier (SPM). A silicon photomultiplier, so-called because of its similarity in performance to conventional photomultiplier tubes, is based on an array of photon counting detectors but with a single common output. While the silicon photomultiplier does not provide positional information, it does allow photon number resolution and photon counting at higher count rates than are achievable with a solitary PCD. These new detectors are enabling a range of new applications in the fields of medicine, biology, high-energy physics and space exploration. In this paper we report the performance of PCD with dimensions ranging from 20 μm × 20 μm to 200 μm × 200 μm and on 1 mm2 silicon photomultipliers and illustrate the use of an SPM in single photon counting mode. [ABSTRACT FROM AUTHOR]

This paper describes the results obtained so far with AquEYE, a single photon counting, fixed aperture photometer for the Asiago 182 cm telescope. AquEYE has been conceived as a prototype of a truly 'quantum' photometer for future Extremely Large Telescopes of 30-50 m aperture. This prototype is characterized by four independent channels equipped with single photon avalanche diodes (SPADs) as detectors. The counts from the four channels are acquired by a TDC board which has a nominal 25 ps time tagging capability. Taking into account the 35 ps jitter in the SPAD itself, the overall precision of the time tags is of the order of 50 ps. The internal oscillator is locked to an external rubidium clock; a GPS pulse per second is collected by the TDC itself to obtain a UTC reference. The maximum photon count rate which the present system can sustain is 12 MHz. [ABSTRACT FROM AUTHOR]

In the framework of a national collaboration to bring Quantum Optics concepts to Astronomy, we are involved in finding suitable detectors for this novel application. At 'INAF Osservatorio Astrofisico di Catania' and 'INFN - Laboratori Nazionali del Sud' laboratories, measurements of electro-optical parameters, such as photon detection efficiency (PDE), linearity, dark counts and after pulsing probability, as well as of timing resolution, have been carried out. These measurements have been done on silicon detectors, such as single photon avalanche diode (SPAD) (both single element and array), and silicon photon multiplier (SiPM), operating in the photon counting regime. [ABSTRACT FROM AUTHOR]

We describe the single-photon counting performance of a hybrid photomultiplier tube (HPMT) near-infrared (950-1300 nm) detector with a transfered electron InGaAsP photocathode and a GaAs Schottky avalanche diode anode. These devices have a lower photoelectron multiplication gain than conventional photomultiplier tubes, but offer a greater linear dynamic range and electrical bandwidth. With the use of a low-noise preamplifier, they can detect single photons with a greater than 20% quantum efficiency (QE) and a reasonably low dark-noise count rate. The avalanche diode at the anode operates in a low gain analog mode and has no afterpulsing. As a result, these HPMTs can detect single photons continuously at high count rates without gating. The relatively large photocathode active area (1 mm diameter) is also attractive to many applications including laser altimetry, ranging, and free-space communications through the atmosphere. We measured 25% photocathode QE and nearly the same single-photon detection efficiency at 1064 nm wavelength with a dark count rate of 60,000 per second at -22°C. The output pulse width in response to single-photon detection is about 0.8 ns. The maximum count rate exceeded 100 million counts per second and was limited only by the speed of the electronics. The rms timing jitter of the HPMT output was measured to be about 0.5 ns. The jitter is dominated by the electron diffusion time within the photocathode and can be improved by reducing the photocathode thickness at a small loss in photocathode QE. We evaluated several of these HPMTs and detailed measurement results are reported in this paper. [ABSTRACT FROM AUTHOR]

Recently developed InGaAs/InP devices suitable as single-photon avalanche diodes (SPADs) in the near-infrared range provide good detection efficiency and low time jitter, together with fairly low dark-count rate at moderately low temperature. However, the overall performance is still severely limited by the afterpulsing effect (due to carriers trapped in deep levels during the avalanche and later released). Experimental studies and speculations aiming to improve the overall performance are here presented. The photon detection efficiency is characterized and the primary dark-count rate is investigated, taking into account thermal generation in the InGaAs layer (absorption layer) and trap-assisted tunneling in the InP layer (multiplication layer). Experimental investigations on the afterpulsing are reported. Improvements obtainable with existing devices by selecting proper operating conditions and circuit solutions are presented and discussed. In order to gain a better insight in the design of new devices, the effectiveness of trapping levels as a function of their location and of the electric field distribution is studied by computer simulation. The fundamental role played by the front-end circuits is assessed and demonstrated, in particular as concerns picosecond photon timing for a SPAD operating in gated-mode with ultrafast gate-on and gate-off transitions. [ABSTRACT FROM AUTHOR]

We report the first resonant-cavity-enhanced single photon avalanche diode (RCE SPAD) fabricated on a reflecting silicon-on-insulator (SOI) substrate. The substrate incorporates a two period distributed Bragg reflector fabricated using a commercially available double SOI process. The RCE SPAD detectors have peak photon detection efficiencies ranging from 42% at 780 nm to 34% at 850 nm and an excellent photon timing resolution of 35 ps full width at half maximum. Despite the higher defectivity of double SOI substrates compared to standard silicon substrates, RCE SPADs with 20 µm diameter exhibit a fairly low dark count rate (DCR) of 3500 cs-1 at room temperature and a yield of 80%. A DCR less than 50 cs-1 can be attained with these detectors by reducing the temperature down to -15°C, while keeping the total afterpulsing probability below 9% with a dead-time of 80 ns. [ABSTRACT FROM AUTHOR]

In life science, optical techniques for the characterization of biological processes are well established and widely used. In most of them, to obtain the best performances, detectors with single-photon detection capability are required. Moreover, the growing demand for this type of information is pushing the technology towards a parallelization of the analysis. These requirements make it very challenging to develop new detection heads, because state-of-the-art detectors, such as photomultiplier tubes (PMTs) and charged coupled devices (CCDs), have some drawbacks. For example, in fluorescence correlation spectroscopy (FCS) fluorescence fluctuations must be monitored on a short time scale because typical time constants range from hundreds of nanoseconds to milliseconds. In this case, developing parallel modules for this application is very challenging. In fact, PMTs are bulky and they cannot be integrated, while the use of imaging detectors, such as CCDs and electron multiplying CCDs, is strongly limited by the read time that determines the minimum correlation time detectable by FCS analysis. We present here a multichannel photon counting module that exploits a monolithic array of single-photon avalanche diodes (SPADs). The detector array consists of eight 50 µm diameter SPADs featuring low dark counting rate and high photon detection efficiency (50% at 550 nm); inter-pixel crosstalk probability is as low as 2 × 10-3. The use of highly integrated active quenching circuits makes it possible to design a very compact read-out circuit, yet providing eight fully independent counting channels operating at high count rate (up to 30 million counts per second). Parallel-mode operation, high count rate and low-cost make this module a potential breakthrough for a widespread diffusion of FCS analysis. [ABSTRACT FROM AUTHOR]

We have presented a scheme to allow photon counting at higher rates than is otherwise possible with existing photon-counting detectors and detection systems. This is done by multiplexing a pool of detectors in a way that greatly suppresses the effect of the deadtimes of the individual detectors. In our previous work we demonstrated the advantage of this approach over simply trying to improve the deadtime of an individual detector or using the type of passively switched system that can be implemented with group of detectors and a tree of beamsplitters. Here, we present an extension of the theoretical modeling of our actively multiplexed scheme to include effects that arise solely from the use of detectors that require gating. We see that such detectors exhibit a deadtime associated with their gate circuitry, independent of whether the detector fires or not, that should be treated separately from the deadtime due to an actual photodetection. In addition, we present experimental results made with an improved switch control system and shorter gate deadtime demonstrating an approximate twofold effective deadtime improvement over our previous demonstration. [ABSTRACT FROM AUTHOR]

We test the performances of an imaging system in revealing either opaque, light diffusing, or transparent objects embedded in tissue phantoms. The method relies on measuring the time-of-flight distributions of near-infrared photons emerging from the phantom within a collection angle of 0.6 mrad about the direction of the incident light by means of a time-correlated single-photon counting apparatus. The apparatus is based on new generation single photon avalanche photodiodes, which are endowed with ≤35 ps resolution, low dark-count rate, short dead time and relatively high quantum efficiency in the near-infrared. The weakly-scattered (ballistic/snake) photons, bringing the relevant image information, are efficiently discriminated from the multiply scattered ones. Thus, the profiles of the embedded objects can be reconstructed and their nature can be assessed. Opaque objects are localized with ≤220 µm spatial resolution. The potential of the new detectors in medical imaging applications is discussed. [ABSTRACT FROM AUTHOR]

InGaAs/InP avalanche photodiodes operated in the so-called Geiger mode currently represent the best solution to detect single-photon beyond 900 nm. They cover the 1100-1650 nm wavelength interval, which includes in particular the two windows used for optical communications (1310 and 1550 nm). A detection efficiency at 1550 nm of 10% with a dark count probability of 10 -5 ns -1 is common, although significant variations can be encountered. At this efficiency, a FWHM temporal response of 300 ps can be achieved. Afterpulses caused by charges trapped by defects in the high field region of the junction constitute the main performance impairment phenomenon. They enhance the dark count probability and reduce out-of-gate detector blindness. These photon counting detectors can be used in optical time-domain reflectometry to improve the spatial resolution and reduce dead-zone effects. Quantum key distribution over metropolitan area networks also constitutes an important application. [ABSTRACT FROM AUTHOR]

A commercial avalanche photodiode (APD) and the circuitry needed to operate it as a single-photon detector (SPD) have been integrated onto a single PC board (PCB). At temperatures accessible with Peltier coolers (∼200-240 K), the PCB-SPD achieves high detection efficiency ( DE ) at 1308 and 1545 nm with low dark-count probability (e.g. ∼10 -6 /bias pulse at DE = 20%, 220 K), making it useful for quantum key distribution (QKD). The board generates fast bias pulses, cancels noise transients, amplifies the signals, and sends them to an on-board discriminator. A digital blanking circuit suppresses afterpulsing. [ABSTRACT FROM AUTHOR]

Experimental results obtained with silicon single photon avalanche diodes (SPADs) in quantum key distribution (QKD) at short wavelengths reveal remarkable potential for application in local area networks (LAN) and for free-space transmission at high rate. Actual application prospects, however, depend on the performance level and on the suitability of practical systems using the available silicon SPAD devices. They can be essentially divided in two groups: planar p-n junction structures with a thin depletion layer (typically 1 μm); and reach-through structures with a thick depletion layer (from 20 μm to 150 μm). The physical mechanisms that control the device behaviour were investigated and the effect on the key parameters of the detector (quantum detection efficiency, dark counting rate, afterpulsing probability and photon-timing jitter) were thoroughly assessed. A quantitative analysis was made of the influence of such parameters on the quantum bit error rate (QBER). Actual parameters were measured and the attainable performance and system suitability of the two device types evaluated. Comparable performance is obtained, but from a system viewpoint thin SPADs appear inherently better suited to high-rate QKD applications, because of their faster response time, ruggedness, low voltage, low power dissipation and fabrication technology, which is simple, efficient, economical and compatible with monolithic integration of detector and associated circuits. [ABSTRACT FROM AUTHOR]

Silicon avalanche photodiodes are the most sensitive photodetectors in the visible to near-infrared region for a wavelength <1000nm. However, when they are used for single photon detection in a Geiger mode, they are known to emit light on the controlled breakdown used to detect a photoelectron. This fluorescence light might have serious impacts on experimental applications like quantum cryptography or single-particle spectroscopy. We characterized the fluorescence behaviour of silicon avalanche photodiodes in the experimentally simple passive quenching configuration and discuss implications for their use in quantum cryptography systems. [ABSTRACT FROM AUTHOR]

The performance of three types of InGaAs/InP avalanche photodiodes is investigated for photon counting at 1550nm in the temperature range of thermoelectric cooling. The best one yields a dark count probability of 2.8 × 10[sup -5] per gate (2.4ns) at a detection efficiency of 10% and a temperature of -60°C. The afterpulse probability and the timing jitter are also studied. The results obtained are compared with those of other papers and applied to the simulation of a quantum key distribution system. An error rate of 10% would be obtained after 54km. [ABSTRACT FROM AUTHOR]

We describe the status of commercially available InGaAs/InP avalanche photodiodes for use as single-photon counters in the telecom wavelength region of 1550nm. [ABSTRACT FROM AUTHOR]