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ABSTRACT: We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy.
Optics Letters 07/2012; 37(14):2877-9. · 3.40 Impact Factor
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Ilaria Bargigia,
Alberto Tosi,
Andrea Bahgat Shehata,
Adriano Della Frera,
Andrea Farina,
Andrea Bassi,
Paola Taroni,
Alberto Dalla Mora, Franco Zappa,
Rinaldo Cubeddu,
Antonio Pifferi
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ABSTRACT: We present a new compact system for time-domain diffuse optical spectroscopy of highly scattering media operating in the wavelength range from 1100 nm to 1700 nm. So far, this technique has been exploited mostly up to 1100 nm: we extended the spectral range by means of a pulsed supercontinuum light source at a high repetition rate, a prism to spectrally disperse the radiation, and a time-gated InGaAs/InP single-photon avalanche diode working up to 1700 nm. A time-correlated single-photon counting board was used as processing electronics. The system is characterized by linear behavior up to absorption values of about 3.4 cm(-1) where the relative error is 17%. A first measurement performed on lipids is presented: the absorption spectrum shows three major peaks at 1200 nm, 1400 nm, and 1700 nm.
Applied Spectroscopy 07/2012; 66(8):944-50. · 1.66 Impact Factor
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Federica Villa,
Bojan Markovic,
Simone Bellisai,
Danilo Bronzi,
Alberto Tosi, Franco Zappa,
Simone Tisa,
Daniel Durini,
Sascha Weyers,
Uwe Paschen,
Werner Brockherde
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ABSTRACT: We present a smart pixel based on a single-photon avalanche diode (SPAD) for advanced time-of-flight (TOF) and time-correlated single photon counting (TCSPC) applications, fabricated in a cost-effective 0.35-um CMOS technology. The large CMOS detector (30-um active area diameter) shows very low noise (12 counts per second at room temperature at 5-V excess bias) and high efficiency in a wide wavelength range (about 50% at 410 nm and still 5% at 800 nm). The analog front-end electronics promptly senses and quenches the avalanche, thus leading to an almost negligible afterpulsing effect. The in-pixel 10-bit time-to-digital converter (TDC) provides 312-ps resolution and 320-ns full-scale range (FSR), i.e., 10-cm single-shot spatial resolution within 50-m depth range in a TOF system. The in-pixel 10-bit memory and output buffers make this smart pixel the viable building block for advanced single-photon imager arrays for 3-D depth ranging in safety and security applications and for 2-D fluorescence lifetime decays in biomedical imaging.
IEEE Photonics Journal 01/2012; 4(3):795-804. · 2.32 Impact Factor
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ABSTRACT: In many time-domain single-photon measurements, wide dynamic range (more than 5 orders of magnitude) is required in short acquisition time (few seconds). We report on the results of a novel technique based on a time-gated Single-Photon Avalanche Diode (SPAD) able to increase the dynamic range of optical investigations. The optical signal is acquired only in well-defined time intervals. Very fast 200-ps gate-ON transition is used to avoid the undesired strong signal, which can saturate the detector, hide the fainter useful signal and reduce the dynamic range. In experimental measurements, we obtained a dynamic range approaching 8 decades in few minutes of acquisition.
Optics Express 05/2011; 19(11):10735-46. · 3.59 Impact Factor
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ABSTRACT: The Rayleigh diffraction bound sets the minimum separation for two point objects to be distinguishable in a conventional imaging system. We demonstrate sub-Rayleigh resolution by scanning a focused beam--in an arbitrary, object-covering pattern that is unknown to the imager--and using N-photon photodetection implemented with a single-photon avalanche detector array. Experiments show resolution improvement by a factor ∼(N-N(max))(½) beyond the Rayleigh bound, where N(max) is the maximum average detected photon number in the image, in good agreement with theory.
Physical Review Letters 10/2010; 105(16):163602. · 7.37 Impact Factor
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Antonio Pifferi,
Alessandro Torricelli,
Lorenzo Spinelli,
Davide Contini,
Rinaldo Cubeddu,
Fabrizio Martelli,
Giovanni Zaccanti,
Alberto Tosi,
Alberto Dalla Mora, Franco Zappa,
Sergio Cova
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ABSTRACT: We demonstrate the feasibility of time-resolved diffuse reflectance measurements at small source-detector separations using a single-photon avalanche diode operated in time-gated mode. Photon time distributions at an interfiber distance of 2 mm were obtained on a homogeneous tissue phantom with a dynamic range of 10(6) and collecting photons at arrival times up to 4 ns. Moreover, we were able to detect a local inhomogeneity deeply buried within a diffusive medium with better spatial resolution, higher signal intensity, and same contrast of a larger (20 mm) interfiber distance. Finally, the proposed approach proved valuable to detect in vivo a task-related brain activation.
Physical Review Letters 04/2008; 100(13):138101. · 7.37 Impact Factor
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ABSTRACT: We present a compact 50 microm x 100 microm cell for single-photon detection, based on a new circuitry monolithically integrated together with a 20 microm-diameter CMOS Single-Photon Avalanche Diode (SPAD). The detector quenching relies on a novel mechanism based on starving the avalanche current till quenching through a variable-load (VLQC, Variable- Load Quenching Circuit). Fabricated in a standard 0.35 microm CMOS technology, the topology allows a SPAD bias voltage higher than the chip supply voltage to be used. Moreover it preserves the advantages of active quenching circuits, in terms of hold-off capability (from 40 ns to 2 micros) and fast reset (</=2 ns), while maintaining the low avalanche charge (</=1.6 pC/avalanche) and extremely small dimensions of passive quenching circuits. The cell enables the development of large-dimension dense arrays of SPADs, for two-dimensional imaging at the photon counting level with photon-timing jitter better than 40 ps.
Optics Express 02/2008; 16(3):2232-44. · 3.59 Impact Factor
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ABSTRACT: 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.
Journal of Modern Optics 01/2007; 54(2-3-54):225-237. · 1.17 Impact Factor
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IEEE T. Instrumentation and Measurement. 01/2006; 55:365-374.
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12/2005: pages 455-460;
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ABSTRACT: A complete module for single-photon counting and timing is demonstrated in a single chip. Features comparable with or better than commercially available macroscopic modules are obtained by integration of an active-quenching and active-reset circuit in complementary metal-oxide semiconductor technology together with a single-photon avalanche diode (SPAD). The integrated SPAD has a 12-microm-diameter sensitive area and operates with an overvoltage above breakdown adjustable up to 20 V. With a 5-V overvoltage the photon detection efficiency peaks above 40% around 500 nm, and the dark-counting rate is lower than 600 counts/s at room temperature. The overall counting dead time is 33 ns.
Optics Letters 07/2005; 30(11):1327-9. · 3.40 Impact Factor
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ABSTRACT: Astrophysical studies require accurate, sensitive and fast detectors to detect faint sources with high variability. Recently an array of Single Photon Avalanche Diodes (SPAD), SPADA, has been developed. This array is suitable for competitive adaptive optics operations and fast transient image acquisition at a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easily integrated with the optics, free from readout noise, and have very fast frame rates (> 10 kHz, for visible corrections) with nanosecond electronic gating. In this paper, the following are described: the development of silicon monolithic arrays of 60 photon-counters, the detection electronics (based on integrated active quenching circuits for each pixel of the array), the real-time data-processing board implemented into FPGA and some aspects of the mechanical housing.
Experimental Astronomy 12/2004; 19(1):163-168. · 1.82 Impact Factor
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IEEE T. Instrumentation and Measurement. 01/2004; 53:163-169.
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Microelectronics Reliability. 01/2003; 43:1669-1674.
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Rinaldo Cubeddu,
Andrea Bassi,
Daniela Comelli,
Sergio Cova,
Andrea Farina,
Massimo Ghioni,
Ivan Rech,
Antonio Pifferi,
Lorenzo Spinelli,
Paola Taroni,
Alessandro Torricelli,
Alberto Tosi,
Gianluca Valentini, Franco Zappa
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ABSTRACT: Light is strictly connected with life, and its presence is fundamental for any living environment. Thus, many biological mechanisms are related to light interaction or can be evaluated through processes involving energy exchange with photons. Optics has always been a precious tool to evaluate molecular and cellular mechanisms, but the discovery of lasers opened new pathways of interactions of light with biological matter, pushing an impressive development for both therapeutic and diagnostic applications in biomedicine. The use of light in different fields has become so widespread that the word photonics has been utilized to identify all the applications related to processes where the light is involved. The photonics area covers a wide range of wavelengths spanning from soft X-rays to mid-infrared and includes all devices related to photons as light sources, optical fibers and light guides, detectors, and all the related electronic equipment. The recent use of photons in the field of telecommunications has pushed the technology toward low-cost, compact, and efficient devices, making them available for many other applications, including those related to biology and medicine where these requirements are of particular relevance. Moreover, basic sciences such as physics, chemistry, mathematics, and electronics have recognized the interdisciplinary need of biomedical science and are translating the most advanced researches into these fields. The Politecnico school has pioneered many of them,and this article reviews the state of the art of biomedical research at the Politecnico in the field internationally known as biophotonics.
IEEE pulse. 2(3):16-23.
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ABSTRACT: Single-molecule spectroscopy is a powerful approach to measuring molecular properties such as size, brightness, conformation, and binding constants. Due to the low concentrations in the single-molecule regime, measurements with good statistical accuracy require long acquisition times. Previously we showed a factor of 8 improvement in acquisition speed using a custom-CMOS 8x1 SPAD array. Here we present preliminary results with a 64X improvement in throughput obtained using a liquid crystal on silicon spatial light modulator (LCOS-SLM) and a novel standard CMOS 1024 pixel SPAD array, opening the way to truly high-throughput single-molecule spectroscopy.
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ABSTRACT: Experimental results obtained with silicon single photon ava-lanche diodes (SPADs) in quantum key distribution (QKD) at short wave-lengths 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 mm); and reach-through structures with a thick depletion layer (from 20 mm to 150 mm). 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 perfor-mance 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 technol-ogy, which is simple, efficient, economical and compatible with monolithic integration of detector and associated circuits.
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Lorenzo Spinelli,
Davide Contini,
Rinaldo Cubeddu,
Antonio Pifferi,
Alessandro Torricelli,
Fabrizio Martelli,
Giovanni Zaccanti,
Alberto Tosi,
Alberto Dalla Mora, Franco Zappa,
Sergio Cova
Photonic Therapeutics and Diagnostics V;
