Fully-integrated CMOS single photon counter

High detection efficiency silicon single-photon detector with a monolithic integrated circuit of active quenching and active reset

Silicon single-photon detectors (SPDs) are key devices for detecting single photons in the visible wavelength range. Photon detection efficiency (PDE) is one of the most important parameters of silicon SPDs, and increasing PDE is highly required for many applications. Here, we present a practical approach to increase the PDE of silicon SPDs with a monolithic integrated circuit of active quenching and active reset (AQAR). The AQAR integrated circuit is specifically designed for thick silicon single-photon avalanche diodes (SPADs) with high breakdown voltage (250 V-450 V) and then fabricated via the process of high-voltage 0.35-μm bipolar-CMOS-DMOS. The AQAR integrated circuit implements the maximum transition voltage of ∼68 V with 30 ns quenching time and 10 ns reset time, which can easily boost PDE to the upper limit by regulating the excess bias up to a high enough level. By using the AQAR integrated circuit, we design and characterize two SPDs with the SPADs disassembled from commercial products of single-photon counting modules (SPCMs). Compared with the original SPCMs, the PDE values are increased from 68.3% to 73.7% and 69.5% to 75.1% at 785 nm, respectively, with moderate increases in dark count rate and afterpulse probability. Our approach can effectively improve the performance of the practical applications requiring silicon SPDs.

Two-photon imaging with silicon photomultipliers

We compared performance of recently developed silicon photomultipliers (SiPMs) to GaAsP photomultiplier tubes (PMTs) for two-photon imaging of neural activity. Despite higher dark counts, SiPMs match or exceed the signal-to-noise ratio of PMTs at photon rates encountered in typical calcium imaging experiments due to their low pulse height variability. At higher photon rates encountered during high-speed voltage imaging, SiPMs substantially outperform PMTs.

Sensors for Positron Emission Tomography Applications

Positron emission tomography (PET) imaging is an essential tool in clinical applications for the diagnosis of diseases due to its ability to acquire functional images to help differentiate between metabolic and biological activities at the molecular level. One key limiting factor in the development of efficient and accurate PET systems is the sensor technology in the PET detector. There are generally four types of sensor technologies employed: photomultiplier tubes (PMTs), avalanche photodiodes (APDs), silicon photomultipliers (SiPMs), and cadmium zinc telluride (CZT) detectors. PMTs were widely used for PET applications in the early days due to their excellent performance metrics of high gain, low noise, and fast timing. However, the fragility and bulkiness of the PMT glass tubes, high operating voltage, and sensitivity to magnetic fields ultimately limit this technology for future cost-effective and multi-modal systems. As a result, solid-state photodetectors like the APD, SiPM, and CZT detectors, and their applications for PET systems, have attracted lots of research interest, especially owing to the continual advancements in the semiconductor fabrication process. In this review, we study and discuss the operating principles, key performance parameters, and PET applications for each type of sensor technology with an emphasis on SiPM and CZT detectors—the two most promising types of sensors for future PET systems. We also present the sensor technologies used in commercially available state-of-the-art PET systems. Finally, the strengths and weaknesses of these four types of sensors are compared and the research challenges of SiPM and CZT detectors are discussed and summarized.

Single-photon avalanche diodes in 0.18-μm high-voltage CMOS technology

We have designed and fabricated high-performance single-photon avalanche diodes (SPADs) by using 0.18-µm high-voltage CMOS technology. Without any technology customization, the SPADs have low dark-count rate, high photon-detection probability, low afterpulsing probability, and acceptable timing jitter and breakdown voltage. Our design provides a low-cost and high-performance SPAD for various applications.

Integrated fiber optical receiver reducing the gap to the quantum limit

Experimental results of a single-photon avalanche diode (SPAD) based optical fiber receiver integrated in 0.35 µm PIN-photodiode CMOS technology are presented. To cope with the parasitic effects of SPADs an array of four receivers is implemented. The SPADs consist of a multiplication zone and a separate thick absorption zone to achieve a high photon detection probability (PDP). In addition cascoded quenchers allow to use a quenching voltage of twice the usual supply voltage, i.e. 6.6 V instead of 3.3 V, in order to increase the PDP further. Measurements result in sensitivities of −55.7 dBm at a data rate of 50 Mbit/s and −51.6 dBm at 100 Mbit/s for a wavelength of 635 nm and a bit-error ratio of 2 × 10⁻³, which is sufficient to perform error correction. These sensitivities are better than those of linear-mode APD receivers integrated in the same CMOS technology. These results are a major advance towards direct detection optical receivers working close to the quantum limit.

Digital holography at light levels below noise using a photon-counting approach

Recording of digital holograms of a weak signal [0.44 counts per second (cps)] hidden below the detector's noise (21 cps) is investigated by employing the high dynamic range of a photon-counting detector. Recording conditions are discussed in terms of the most important holographic measures, namely, the fringe visibility (or contrast) and signal-to-noise ratio (SNR), and in relation to the main holographic parameters. Theoretically evaluated curves are tested by recording holograms for a wide range of the parameter values. We found that (i) the optimum set of holographic parameters can be determined for a harsh signal conditions, (ii) increasing the visibility does not necessarily improve the more important SNR, and (iii) in cases of nearly constant visibility, the SNR clearly reveals differences in the quality of holographic recordings.

Using Permutations to Enhance the Gain of RUQB Technique

Quantum key distribution (QKD) techniques usually suffer from a gain problem when comparing the final key to the generated pulses of quantum states. This research permutes the sets that RUQB (Abu-ayyash & Ajlouni, 2008) uses in order to increase the gain. The effect of both randomness and permutations are studied; While RUQB technique improves the gain of BB84 QKD by 5.5% it was also shown that the higher the randomness of the initial key the higher the gain that can be achieved, this work concluded that the use of around 7 permutations results in 30% gain recovery in an ideal situations.

Analog single-photon counter for high-speed scanning microscopy

We introduce a novel single-photon sensitive photodetection method of analog single-photon counting (SPC) for the application of high-speed scanning microscopy that requires high measurement speed and wide dynamic range for the photodetector. This scheme is based on analog electronic circuits which can perform proper differentiation and integration operations before and after discrimination of the analog signal from the photomultiplier tube (PMT), respectively. In spite of its simpler implementation, our analog SPC scheme exhibits good sensitivity and operation stability. Related with the dynamic range, the maximum count rate of our analog SPC is significantly improved due to the fast operation of the analog circuitry. This characteristic of the higher counting rate makes this scheme very suitable for high-speed scanning microscopy. It has also been demonstrated that the afterpulsing problem of an analog-mode PMT is the major noise source that degrades the image quality in the application of scanning microscopy, and our SPC scheme successfully neutralizes this kind of impulse noises to obtain a nearly shot-noise-limited imaging performance.

Performance trade-offs in single-photon avalanche diode miniaturization

Single-photon avalanche diodes (SPADs) provide photons' time of arrival for various applications. In recent years, attempts have been made to miniaturize SPADs in order to facilitate large-array integration and in order to reduce the dead time of the device. We investigate the benefits and drawbacks of device miniaturization by characterizing a new fast SPAD in a commercial 0.18 microm complementary metal oxide semiconductor technology. The device employs a novel and efficient guard ring, resulting in a high fill factor. Thanks to its small size, the dead time is only 5 ns, resulting in the fastest reported SPAD to date. However, the short dead time is accompanied by a high after-pulsing rate, which we show to be a limiting parameter for SPAD miniaturization. We describe a new and compact active-recharge scheme which improves signal-to-noise tenfold compared with the passive configuration, using a fraction of the area of state-of-the-art active-recharge circuits, and without increasing the dead time. The performance of compact SPADs stands to benefit such applications as high-resolution fluorescence-lifetime imaging, active-illumination three-dimensional imagers, and quantum key distribution systems.