A single photon receiver module combining an InGaAsP/InP avalanche photodiode with peak responsivity at 1064nm
and a CMOS integrated electronic circuit for operation in both gated and free running modes is presented. The standalone
module exhibits a single photon detection probability as high as 30% at 1064nm that is by far higher than silicon
devices. The dark count rate mean value over eight devices cooled down to -40°C is about 100Hz at 7.5% detection
probability and 1.2kHz at 30%. Dark count rate versus temperature measurements show that trap-assisted tunneling in
the InP multiplication layer progressively dominates the total dark count rate when the device is cooled down. At
medium cooling, the thermal generation in the absorber is the dominant mechanism. Afterpulsing rate is relatively high
when compared to silicon devices. However, the integration of a dedicated pulser in close-proximity with the APD
makes possible free-running operation. The timing resolution was measured at 430ps FWHM at 30% detection
probability. Though comparing favorably with silicon reach-through avalanche photodiodes, we believe that a large
uncertainty stands on this measurement. A timing resolution of less than 300ps is expected with the developed receiver
module.
Single photon detection at telecom wavelengths is of importance in many industrial applications ranging from quantum
cryptography, quantum optics, optical time domain reflectometry, non-invasive testing of VLSI circuits, eye-safe
LIDAR to laser ranging. In practical applications, the combination of an InGaAs/InP APD with an appropriate
electronic circuit still stands as the best solution in comparison with emerging technologies such as superconducting
single photon detectors, MCP-PMTs for the near IR or up-conversion technique.
An ASIC dedicated to the operation of InGaAs/InP APDs in both gated mode and free-running mode is presented. The
1.6mm2 chip is fabricated in a CMOS technology. It combines a gate generator, a voltage limiter, a fast comparator, a
precise timing circuit for the gate signal processing and an output stage. A pulse amplitude of up to +7V can be
achieved, which allows the operation of commercially available APDs at a single photon detection probability larger
than 25% at 1.55&mgr;m. The avalanche quenching process is extremely fast, thus reducing the afterpulsing effects. The
packaging of the diode in close proximity with the quenching circuit enables high speed gating at frequencies larger
than 10MHz. The reduced connection lengths combined with impedance adaptation technique provide excellent gate
quality, free of oscillations or bumps. The excess bias voltage is thus constant over the gate width leading to a stable
single photon detection probability and timing resolution. The CMOS integration guarantees long-term stability,
reliability and compactness.
A compact single photon detector designed for the detection in the visible spectral range is presented. A fast active quenching circuit is integrated on the chip in order to operate the APD in single photon counting mode. The sensor consists of a 0.8x0.8mm2 silicon chip mounted on a thermo-electric cooler and packaged in a standard TO5 header, bringing the degree of miniaturization to a level never reached. Reliability, compactness, low power and low cost make the detector essential for portable devices, implantable sensors, fluorescence lifetime spectrometers or laser scanning microscopes. In addition, the sensor exhibits best-in-class timing resolution of 50ps. The photon detection probability peaks in the blue/green at almost 35% and is limited to a few percents in the red and near-infrared regions. When cooled down to -10°C, the 50μm diameter diode achieves a dark count rate lower than 10Hz. The afterpulsing is maintained to a low level, below 1%. The fast active quenching circuit leads to a dead time of 50ns allowing a measurement frequency of up to 20MHz. The detector, unlike legacy photon counters, does not suffer from memory effects and is not damaged by ambient light.
We present parallel single molecule detection (SMD) and fluorescence correlation spectroscopy (FCS) experiments with a fully integrated complementary metal oxide semiconductor (CMOS) single-photon 2×2 detector array. Multifocal excitation is achieved with a diffractive optical element (DOE). Special emphasis is placed on parallelization of the total system. The performance of the novel single-photon CMOS detector is investigated and compared to a state-of-the-art single-photon detecting module [having an actively quenched avalanche photodiode (APD)] by measurements on free diffusing molecules at different concentrations. Despite the order of magnitude lower detection efficiency of the CMOS detector compared to the state-of-the-art single-photon detecting module, we achieve single molecule sensitivity and reliably determine molecule concentrations. In addition, the CMOS detector performance for the determination of the fraction of slowly diffusing molecules in a primer solution (two-component analysis) is demonstrated. The potential of this new technique for high-throughput confocal-detection-based systems is discussed.
We present multipoint Fluorescence Correlation Spectroscopy (FCS) experiments with a fully integrated Complementary Metal Oxide Semiconductor (CMOS) single photon 2x2 detector array. Multifocal excitation was achieved with a diffractive optical element (DOE). Special emphasis was put on parallelization of the total system. In particular the performance of the single-photon CMOS detector was investigated and compared to a state-of-the art single-photon detecting module (actively quenched avalanche photo diode) by measurements on free diffusing molecules at different concentrations. The potential of our new technique for high throughput FCS based systems is discussed.
Monitoring biological relevant reactions on the single molecule level by the use of fluorescent probes has become one of the most promising approaches for understanding a variety of phenomena in living organisms. By applying techniques of fluorescence spectroscopy to labelled molecules a manifold of different parameters becomes accessible i.e. molecular dynamics, energy transfer, DNA fingerprinting, etc... can be monitored at the molecular level.
However, many of these optical methods rely on oversimplified assumptions, for example a three-dimensional Gaussian observation volume, perfect overlap volume for different wavelength, etc. which are not valid approximations under many common measurement conditions. As a result, these measurements will contain significant, systematic artifacts, which limit their performance and information content.
Based on Fluorescence Correlation Spectroscopy (FCS) and Fluorescence Lifetime Spectroscopy we will present representative examples including a thorough signal analysis with a strong emphasis on the underlying optical principles and limitations. An outlook to biochip applications, parallel FCS and parallel Lifetime measurements will be given with cross links to optical concepts and technologies used in industrial inspection.
A passively quenched single photon counting avalanche diode (PQ-SPAD) is integrated in a conventional CMOS process. Co-integration of passive quenching circuit and photodiode leads to a robust pulse and a dead time as low as 32ns. The FWHM timing resolution of the PQ-SPAD is 50ps. The 30mm2 photosensitive area photodiode has a maximum photon detection probability about 20% at λ=460nm, 5% at λ=700nm and 1% at λ=900nm. The dark count rate is 300Hz at room temperature and follows a poissonian distribution. By a cooling of the detector at -20°C, a dark count rate in the 10Hz range can be obtained. The afterpulsing probability is 2.5% at room temperature with 80% of the afterpulses located in the first 100ns after the avalanche event. The PQ-SPAD is well suited for detection applications in the visible and near infrared wavelengths and where the light can be concentrated on the active area using a high magnification objective. The PQ-SPAD also offers gated operation possibility for applications where the arrival of the photons is known. Due to its outstanding characteristics obtained at very low cost, the PQ-SPAD element opens the way to integration of detector arrays.
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