RESUMEN
One major drawback of the classic time-correlated single photon counting (TCSPC) technique is pileup-related distortion. To keep it under a reasonable level, the maximum count rate has to be reduced, posing a serious limitation to the overall measurement speed. This means that there is an intrinsic trade-off between speed and distortion: either count rate is raised, but distortion is worsened, or distortion is minimized at the expense of speed. In both cases, it is impossible to precisely evaluate the degree of distortion introduced. Here comes our new, to the best of our knowledge, figure of merit, which is able to provide a numerical estimate of the distortion whatever the signal shape is, marking a real turning point in the way of doing TCSPC. In this article, this new parameter will be defined and its effectiveness will be demonstrated by means of mathematical computations.
RESUMEN
Picosecond timing of single photons has laid the foundation of a great variety of applications, from life sciences to quantum communication, thanks to the combination of ultimate sensitivity with a bandwidth that cannot be reached by analog recording techniques. Nowadays, more and more applications could still be enabled or advanced by progress in the available instrumentation, resulting in a steadily increasing research interest in this field. In this scenario, single-photon avalanche diodes (SPADs) have gained a key position, thanks to the remarkable precision they are able to provide, along with other key advantages like ruggedness, compactness, large signal amplitude, and room temperature operation, which neatly distinguish them from other solutions like superconducting nanowire single-photon detectors and silicon photomultipliers. With this work, we aim at filling a gap in the literature by providing a thorough discussion of the main design rules and tradeoffs for silicon SPADs and the electronics employed along them to achieve high timing precision. In the end, we conclude with our outlook on the future by summarizing new routes that could benefit from present and prospective timing features of silicon SPADs.
RESUMEN
One of the major drawbacks of time-correlated single-photon counting (TCSPC) is generally represented by pile-up distortion, which strongly bounds the maximum acquisition speed to a few percent of the laser excitation rate. Based on a previous theoretical analysis, recently we presented the first, to the best of our knowledge, low-distortion and high-speed TCSPC system capable of overcoming the pile-up limitation by perfectly matching the single-photon avalanche diode (SPAD) dead time to the laser period. In this work, we validate the proposed system in a standard fluorescence measurement by comparing experimental data with the reference theoretical framework. As a result, a count rate of 32 Mc/s was achieved with a single-channel system still observing a negligible lifetime distortion.
RESUMEN
Multispectral/hyperspectral fluorescence lifetime imaging microscopy (λFLIM) is a promising tool for studying functional and structural biological processes. The rich information content provided by a multidimensional dataset is often in contrast with the acquisition speed. In this work, we develop and experimentally demonstrate a wide-field λFLIM setup, based on a novel time-resolved 18×1 single-photon avalanche diode array detector working in a single-pixel camera scheme, which parallelizes the spectral detection, reducing measurement time. The proposed system, which implements a single-pixel camera with a compressive sensing scheme, represents an optimal microscopy framework towards the design of λFLIM setups.
RESUMEN
We present an optical depth imaging system suitable for highly scattering underwater environments. The system used the time-correlated single-photon counting (TCSPC) technique and the time-of-flight approach to obtain depth profiles. The single-photon detection was provided by a linear array of single-photon avalanche diode (SPAD) detectors fabricated in a customized silicon fabrication technology for optimized efficiency, dark count rate, and jitter performance. The bi-static transceiver comprised a pulsed laser diode source with central wavelength 670 nm, a linear array of 16 × 1 Si-SPAD detectors, with a dedicated TCSPC acquisition module. Cylindrical lenses were used to collect the light scattered by the target and image it onto the sensor. These laboratory-based experiments demonstrated single-photon depth imaging at a range of 1.65 m in highly scattering conditions, equivalent up to 8.3 attenuation lengths between the system and the target, using average optical powers of up to 15 mW. The depth and spatial resolution of this sensor were investigated in different scattering conditions.
RESUMEN
Time-Correlated Single Photon Counting (TCSPC) is an essential tool in many scientific applications, where the recording of optical pulses with picosecond precision is required. Unfortunately, a key issue has to be faced: distortion phenomena can affect TCSPC experiments at high count rates. In order to avoid this problem, TCSPC experiments have been commonly carried out by limiting the maximum operating frequency of a measurement channel below 5% of the excitation frequency, leading to a long acquisition time. Recently, it has been demonstrated that matching the detector dead time to the excitation period allows to keep distortion around zero regardless of the rate of impinging photons. This solution paves the way to unprecedented measurement speed in TCSPC experiments. In this scenario, the front-end circuits that drive the detector play a crucial role in determining the performance of the system, both in terms of measurement speed and timing performance. Here we present two fully integrated front-end circuits for Single Photon Avalanche Diodes (SPADs): a fast Active Quenching Circuit (AQC) and a fully-differential current pick-up circuit. The AQC can apply very fast voltage variations, as short as 1.6ns, to reset external custom-technology SPAD detectors. A fast reset, indeed, is a key parameter to maximize the measurement speed. The current pick-up circuit is based on a fully differential structure which allows unprecedented rejection of disturbances that typically affect SPAD-based systems at the end of the dead time. The circuit permits to sense the current edge resulting from a photon detection with picosecond accuracy and precision even a few picoseconds after the end of the dead time imposed by the AQC. This is a crucial requirement when the system is operated at high rates. Both circuits have been deeply characterized, especially in terms of achievable measurement speed and timing performance.
RESUMEN
Single photon avalanche diodes (SPADs) have been subject to a fast improvement in recent years. In particular, custom technologies specifically developed to fabricate SPAD devices give the designer the freedom to pursue the best detector performance required by applications. A significant breakthrough in this field is represented by the recent introduction of a red enhanced SPAD (RE-SPAD) technology, capable of attaining a good photon detection efficiency in the near infrared range (e.g. 40% at a wavelength of 800 nm) while maintaining a remarkable timing resolution of about 100ps full width at half maximum. Being planar, the RE-SPAD custom technology opened the way to the development of SPAD arrays particularly suited for demanding applications in the field of life sciences. However, to achieve such excellent performance custom SPAD detectors must be operated with an external active quenching circuit (AQC) designed on purpose. Next steps toward the development of compact and practical multichannel systems will require a new generation of monolithically integrated AQC arrays. In this paper we present a new, fully integrated AQC fabricated in a high-voltage 0.18 µm CMOS technology able to provide quenching pulses up to 50 Volts with fast leading and trailing edges. Although specifically designed for optimal operation of RE-SPAD devices, the new AQC is quite versatile: it can be used with any SPAD detector, regardless its fabrication technology, reaching remarkable count rates up to 80 Mcounts/s and generating a photon detection pulse with a timing jitter as low as 119 ps full width at half maximum. The compact design of our circuit has been specifically laid out to make this IC a suitable building block for monolithically integrated AQC arrays.
RESUMEN
At the present time, Single Photon Avalanche Diodes (SPADs) are the enabling devices in many applications, ranging from medical imaging to laser ranging and from remote sensing to quantum key distribution. Even though they belong to different scientific domains, these applications share the need for a detector capable of attaining high count rates possibly without trading it off with other key detector's features, such as afterpulsing probability, photon detection efficiency, and dark counts. In this work, we present the characterization of a fast integrated active quenching circuit capable of driving high-performance external custom-technology SPADs for single photon detection in the visible wavelength range. Combining the prompt intervention of the electronic circuitry and the performance of a custom-technology SPAD, we attained count rates up to 250 MCps while keeping the afterpulsing probability within 2%.