S. Tisa

Politecnico di Milano, Milano, Lombardy, Italy

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Publications (75)67.72 Total impact

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    ABSTRACT: We present a Time-to-Digital Converter (TDC) card with a compact form factor, suitable for multichannel timing instruments or for integration into more complex systems. The TDC Card provides 10 ps timing resolution over the whole measurement range, which is selectable from 160 ns up to 10 μs, reaching 21 ps rms precision, 1.25% LSB rms differential nonlinearity, up to 3 Mconversion/s with 400 mW power consumption. The I/O edge card connector provides timing data readout through either a parallel bus or a 100 MHz serial interface and further measurement information like input signal rate and valid conversion rate (typically useful for time-correlated single-photon counting application) through an independent serial link.
    The Review of scientific instruments. 11/2014; 85(11):114703.
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    ABSTRACT: We report on the design and characterization of a multipurpose 64x32CMOS single-photon avalanche diode (SPAD) array. The chip is fabricated in a high-voltage 0.35-μm CMOS technology and consists of 2048 pixels, each combining a very low noise (100 cps at 5-V excess bias) 30-μm SPAD, a prompt avalanche sensing circuit, and digital processing electronics. The array not only delivers two-dimensional intensity information through photon counting in either free-running (down to 10-μs integration time) or time-gated mode, but can also perform smart light demodulation with in-pixel background suppression. The latter feature enables phase-resolved imaging for extracting either three-dimensional depth-resolved images or decay lifetime maps, by measuring the phase shift between a modulated excitation light and the reflected photons. Pixel-level memories enable fully parallel processing and global-shutter readout, preventing motion artifacts (e.g., skew, wobble, motion blur) and partial exposure effects. The array is able to acquire very fast optical events at high frame-rate (up to 100 000 fps) and at single-photon level. Low-noise SPADs ensure high dynamic range (up to 110 dB at 100 fps) with peak photon detection efficiency of almost 50% at 410 nm. The SPAD imager provides different operating modes, thus, enabling both time-domain applications, like fluorescence lifetime imaging (FLIM) and fluorescence correlation spectroscopy, as well as frequency-domain FLIM and lock-in 3-D ranging for automotive vision and lidar.
    IEEE Journal of Selected Topics in Quantum Electronics 11/2014; 20(6). · 4.08 Impact Factor
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    ABSTRACT: We present a CMOS imager consisting of 32×32 smart pixels, each one able to detect single photons in the 300-900 nm wavelength range and to perform both photon-counting and photon-timing operations on very fast optical events with faint intensities. In photon-counting mode, the imager provides photon-number (i.e, intensity) resolved movies of the scene under observation, up to 100 000 frames/s. In photon-timing, the imager provides photon arrival times with 312 ps resolution. The result are videos with either time-resolved (e.g., fluorescence) maps of a sample, or 3-D depth-resolved maps of a target scene. The imager is fabricated in a cost-effective 0.35-μm CMOS technology, automotive certified. Each pixel consists of a single-photon avalanche diode with 30 μm photoactive diameter, coupled to an in-pixel 10-bit time-to-digital converter with 320-ns full-scale range, an INL of 10% LSB and a DNL of 2% LSB. The chip operates in global shutter mode, with full frame times down to 10 μs and just 1-ns conversion time. The reconfigurable imager design enables a broad set of applications, like time-resolved spectroscopy, fluorescence lifetime imaging, diffusive optical tomography, molecular imaging, time-of-flight 3-D ranging and atmospheric layer sensing through LIDAR.
    IEEE Journal of Selected Topics in Quantum Electronics 09/2014; 20(6). · 4.08 Impact Factor
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    ABSTRACT: The double-slit experiment strikingly demonstrates the wave-particle duality of quantum objects. In this famous experiment, particles pass one-by-one through a pair of slits and are detected on a distant screen. A distinct wave-like pattern emerges after many discrete particle impacts as if each particle is passing through both slits and interfering with itself. Here we present a temporally- and spatially-resolved measurement of the double-slit interference pattern using single photons. We send single photons through a birefringent double-slit apparatus and use a linear array of single-photon detectors to observe the developing interference pattern. The analysis of the buildup allows us to compare quantum mechanics and the corpuscular model, which aims to explain the mystery of single-particle interference. Finally, we send one photon from an entangled pair through our double-slit setup and show the dependence of the resulting interference pattern on the twin photon's measured state. Our results provide new insight into the dynamics of the buildup process in the double-slit experiment, and can be used as a valuable resource in quantum information applications.
    Scientific Reports 04/2014; 4:4685. · 5.08 Impact Factor
  • SPIE Sensing Technology+ Applications; 01/2014
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    ABSTRACT: 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.
    Journal of Modern Optics 12/2013; 61(2). · 1.16 Impact Factor
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    ABSTRACT: We present a compact time-resolved spectrometer suitable for optical spectroscopy from 400 nm to 1 μm wavelengths. The detector consists of a monolithic array of 16 high-precision Time-to-Digital Converters (TDC) and Single-Photon Avalanche Diodes (SPAD). The instrument has 10 ps resolution and reaches 70 ps (FWHM) timing precision over a 160 ns full-scale range with a Differential Non-Linearity (DNL) better than 1.5 % LSB. The core of the spectrometer is the application-specific integrated chip composed of 16 pixels with 250 μm pitch, containing a 20 μm diameter SPAD and an independent TDC each, fabricated in a 0.35 μm CMOS technology. In front of this array a monochromator is used to focus different wavelengths into different pixels. The spectrometer has been used for fluorescence lifetime spectroscopy: 5 nm spectral resolution over an 80 nm bandwidth is achieved. Lifetime spectroscopy of Nile blue is demonstrated.
    12/2013
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    ABSTRACT: We developed a single-photon counting multichannel detection system, based on a monolithic linear array of 32 CMOS SPADs (Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Diodes). All channels achieve a timing resolution of 100 ps (full-width at half maximum) and a photon detection efficiency of 50% at 400 nm. Dark count rate is very low even at room temperature, being about 125 counts/s for 50 μm active area diameter SPADs. Detection performance and microelectronic compactness of this CMOS SPAD array make it the best candidate for ultra-compact time-resolved spectrometers with single-photon sensitivity from 300 nm to 900 nm.
    The Review of scientific instruments 12/2013; 84(12):123112. · 1.52 Impact Factor
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    ABSTRACT: An estimation and remote state preparation for qubits are demonstrated by implementing a 28 element quantum measurement using an array of detectors and carefully designed imaging optics.
    CLEO: QELS_Fundamental Science; 06/2013
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    ABSTRACT: We experimentally demonstrate a quantum state estimation and tomography for qubits encoded in a single photon's spatial degree of freedom. The experimental setup depicted in Fig. 1 consists of: 1) polarization entangled photon pairs source; 2) spatial encoder allowing to map a polarization state into spatial state; 3) polarization analyzer and 4) spatial state analyzer. The 28 element spatial quantum state measurement set was implemented using imaging optics and a linear array of 28 single photon avalanche diodes (SPAD). The timing information from all the detectors was acquired using custom made FPGA electronics.
    International Quantum Electronics Conference; 05/2013
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    ABSTRACT: SPADs (Single Photon Avalanche Diodes) are emerging as most suitable photodetectors for both single-photon counting (Fluorescence Correlation Spectroscopy, Lock-in 3D Ranging) and single-photon timing (Lidar, Fluorescence Lifetime Imaging, Diffuse Optical Imaging) applications. Different complementary metal-oxide semiconductor (CMOS) implementations have been reported in literature. We present some figure of merit able to summarize the typical SPAD performances (i.e. Dark Counting Rate, Photo Detection Efficiency, afterpulsing probability, hold-off time, timing jitter) and to identify a proper metric for SPAD comparison, both as single detectors and also as imaging arrays. The goal is to define a practical framework within which it is possible to rank detectors based on their performances in specific experimental conditions, for either photon-counting or photon-timing applications. Furthermore we review the performances of some CMOS and custom-made SPADs. Results show that CMOS SPADs performances improve as the technology scales down; moreover, miniaturization of SPADs and new solutions adopted to counteract issues related with the SPAD design (electric field uniformity, premature edge breakdown, tunneling effects, defect-rich STI interface) along with advances in standard CMOS processes led to a general improvement in all fabricated photodetectors; therefore, CMOS SPADs can be suitable for very dense and cost-effective many-pixels imagers with high performances.
    Proc SPIE 05/2013;
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    ABSTRACT: "Indirect" time-of-flight is one technique to obtain depth-resolved images through active illumination that is becoming more popular in the recent years. Several methods and light timing patterns are used nowadays, aimed at improving measurement precision with smarter algorithms, while using less and less light power. Purpose of this work is to present an indirect time-of-flight imaging camera based on pulsed-light active illumination and a 32 × 32 single-photon avalanche diode array with an improved illumination timing pattern, able to increase depth resolution and to reach single-photon level sensitivity.
    Optics Express 02/2013; 21(4):5086-5098. · 3.55 Impact Factor
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    ABSTRACT: We present a photon-counting module based on InGaAs/InP SPAD (Single-Photon Avalanche Diode) for detecting single photons up to 1.7 μm. The module exploits a novel architecture for generating and calibrating the gate width, along with other functions (such as module supervision, counting and processing of detected photons, etc.). The gate width, i.e. the time interval when the SPAD is ON, is user-programmable in the range from 500 ps to 1.5 μs, by means of two different delay generation methods implemented with an FPGA (Field-Programmable Gate Array). In order to compensate chip-to-chip delay variation, an auto-calibration circuit picks out a combination of delays in order to match at best the selected gate width. The InGaAs/InP module accepts asynchronous and aperiodic signals and introduces very low timing jitter. Moreover the photon counting module provides other new features like a microprocessor for system supervision, a touch-screen for local user interface, and an Ethernet link for smart remote control. Thanks to the fullyprogrammable and configurable architecture, the overall instrument provides high system flexibility and can easily match all requirements set by many different applications requiring single photon-level sensitivity in the near infrared with very low photon timing jitter.
    Proc SPIE 01/2013;
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    ABSTRACT: We present a single-photon avalanche diode (SPAD) front-end circuitry, in a cost-effective 0.35 $mu{rm m}$ CMOS technology, for single-photon detection in the visible wavelength range, aimed at speeding up the sensing of detector ignition and at promptly quenching the avalanche current buildup. The circuit allows the reduction in detrimental effects of afterpulsing through reducing any delays in the electronics intervention on the detector and through a proper time-varying action of the MOS transistors on the different SPAD's operating conditions. The sensing time is reduced down to a few hundreds of picoseconds, with an active quenching transition of about 1 ns for 6 V excess bias, and a final reset in just 3 ns.
    IEEE Photonics Technology Letters 01/2013; 25(8):776-779. · 2.04 Impact Factor
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    ABSTRACT: We designed and characterized Silicon Single-Photon Avalanche Diodes (SPADs) fabricated in a high-voltage 0.35 μm CMOS technology, achieving state-of-the-art low Dark Counting Rate (DCR), very large diameter, and extended Photon Detection Efficiency (PDE) in the Near Ultraviolet. So far, different groups fabricated CMOS SPADs in scaled technologies, but with many drawbacks in active area dimensions (just a few micrometers), excess bias (just few Volts), DCR (many hundreds of counts per second, cps, for small 10 μm devices) and PDE (just few tens % in the visible range). The novel CMOS SPAD structures with 50 μm, 100 μm, 200 μm and 500 μm diameters can be operated at room temperature and show DCR of 100 cps, 2 kcps, 20 kcps and 100 kcps, respectively, even when operated at 6 V excess bias. Thanks to the excellent performances, these large CMOS SPADs are exploitable in monolithic SPAD-based arrays with on-chip CMOS electronics, e.g. for time-resolved spectrometers with no need of microlenses (thanks to high fillfactor). Instead the smaller CMOS SPADs, e.g. the 10 μm devices with just 3 cps at room temperature and 6 V excess bias, are the viable candidates for dense 2D CMOS SPAD imagers and 3D Time-of-Flight ranging chips.
    Proc SPIE 01/2013;
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    ABSTRACT: This paper presents a time-to-digital converter (TDC) architecture capable of reaching high-precision and high-linearity with moderate area occupation per measurement channel. The architecture is based on a coarse counter and a couple of two-stage interpolators that exploit the cyclic sliding scale technique in order to improve the conversion linearity. The interpolators are based on a new coarse-fine synchronization circuit and a new single-stage Vernier delay loop fine interpolation. In a standard cost-effective 0.35 μm CMOS technology the TDC reaches a dynamic range of 160 ns, 17.2 ps precision and differential non-linearity better than 0.9% LSB rms. The TDC building block was designed in order to be easily assembled in a multi-channel monolithic TDC chip. Coupled with a SPAD photodetector it is aimed for TCSPC applications (like FLIM, FCS, FRET) and direct ToF 3-D ranging.
    Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2013; 60(3):557-569. · 2.24 Impact Factor
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    ABSTRACT: We present a compact TDC Module based on the Time-to-Digital Converter ASIC fabricated in 0.35 μm CMOS technology. This chip measures the time-interval between two inputs, called START and STOP, with a 10 ps resolution when using a 10 ns reference clock. Thanks to the structure, composed by two independent “interpolators” for each input and a “coarse” counter, the TDC chip can reach an average precision better than 15 psRMS and a differential non-linearity (DNL) smaller than 0.9 %LSB with a maximum conversion rate of about 3 Msps. A simple calibration allows to compute proper coefficients to apply to raw data. The TDC Module is composed by two SMA inputs, followed by an electronic front-end to provide compatibility to any kind of signal, an USB 2.0 connector for parameters setting and data upload to a remote computer and the power supply connector.
    Time-to-Digital Converters (NoMe TDC), 2013 IEEE Nordic-Mediterranean Workshop on; 01/2013
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    ABSTRACT: A CMOS imager that combines single photon sensitivity with photon timing capabilities has been developed for Time-Of-Flight (TOF) measurements and for Time-Correlated Single-Photon Counting (TCSPC) applications. A test structure with 32×4 pixels is presented in this paper. Each pixel is based on a 30 μm diameter Single-Photon Avalanche Diode (SPAD) with low Dark Counting Rate (60 cps at room temperature) and a Time-to-Digital Converter (TDC) with 400 ps resolution. Some preliminary measurements confirm the possibility to use this SPAD array in a 3D TOF scanning system.
    Time-to-Digital Converters (NoMe TDC), 2013 IEEE Nordic-Mediterranean Workshop on; 01/2013
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    ABSTRACT: The growing interest for fast, compact and cost-effective 3D ranging imagers for automotive applications has prompted to explore many different techniques for 3D imaging and to develop new system for this propose. CMOS imagers that exploit phase-resolved techniques provide accurate 3D ranging with no complex optics and are rugged and costeffective. Phase-resolved techniques indirectly measure the round-trip return of the light emitted by a laser and backscattered from a distant target, computing the phase delay between the modulated light and the detected signal. Singlephoton detectors, with their high sensitivity, allow to actively illuminate the scene with a low power excitation (less than 10W with diffused daylight illumination). We report on a 4x4 array of CMOS SPAD (Single Photon Avalanche Diodes) designed in a high-voltage 0.35 μm CMOS technology, for pulsed modulation, in which each pixel computes the phase difference between the laser and the reflected pulse. Each pixel comprises a high-performance 30 μm diameter SPAD, an analog quenching circuit, two 9 bit up-down counters and memories to store data during the readout. The first counter counts the photons detected by the SPAD in a time window synchronous with the laser pulse and integrates the whole echoed signal. The second counter accumulates the number of photon detected in a window shifted with respect to the laser pulse, and acquires only a portion of the reflected signal. The array is readout with a global shutter architecture, using a 100 MHz clock; the maximal frame rate is 3 Mframe/s.
    Proc SPIE 10/2012;
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    ABSTRACT: Combined 2D imaging and 3D ranging sensors provide useful information for both long (some kms) and short (few tens of m) distance, in security applications. To this aim, we designed two different monolithic imagers in a 0.35 μm costeffective CMOS technology, based on Single Photon Avalanche Diodes (SPADs), for long-range time-of-flight (TOF) and short-range phase-resolved depth ranging. The single pixel consists of a SPAD (30 μm diameter), a quenching circuit, and a Time-to-Digital Converter (TDC) for TOF measurements or three up/down synched counters for phaseresolved depth assessments. Such smart pixels operate in two different modalities: single photon-counting for 2D "intensity" images; while either photon-timing or phase-resolved photon-counting for 3D "depth" images. In 2D imaging, each pixel has a counter that accumulates the number of photons detected by the SPAD in the pixel, thus providing single-photon level sensitivity and high (100 kframe/s) frame-rate. In the TOF 3D imager, each pixel measures the photon arrival time with a 312 ps resolution, thanks to a two-stage TDC (with 6 bit coarse counter plus a 4 bit fine interpolator), with a 320 ns full-scale range. The resulting spatial resolution is 9 cm within a 50 m range, centered at any user-selectable distance (e.g. 100 m - 5 km), with linearity of DNLrms=4.9% LSB and INLrms=11.7% LSB, and 175 ps precision. In the phase-resolved 3D imager, the in-pixel electronics measures the phase difference between the modulated light emitted by a laser and the back-reflected light, with both continuous-wave and pulsed-light modulation techniques.
    Proc SPIE 09/2012;