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ABSTRACT: In free-space single-photon quantum key distribution (QKD), the error rate due to daytime background photons can be reduced with strong temporal filtering. In this case, the improvement in performance is determined by the receiver's ability to resolve signal-photon arrival times. We use fast clock recovery and commercially available single-photon detectors with timing resolution enhanced by additional electronic circuitry to implement temporal gating down to 50 ps in a free-space QKD system. The single-photon channel operates at 850 nm, and the improved timing resolution enables transmission rates of 1.25 GHz. We observe daytime quantum bit error rates of 0.04, which is less than one-third of the ungated error rate. We present the design and performance of the system and demonstrate its benefit to free-space QKD.
IEEE Journal of Selected Topics in Quantum Electronics 11/2010; · 3.78 Impact Factor
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ABSTRACT: Recent advances in fluorescence measurements for single molecule spectroscopy, genomics, proteomics and medical diagnostics require single-photon detectors with high quantum efficiency in the extended red spectral range (from 600 nm to 900 nm) and low noise (<50 kc s−1). Amongst industrial production, avalanche photodiodes with large diameter (up to 500 µm) are available which can work in Geiger mode (GM) with good photon detection efficiency (higher than 20%) and some of them also with quite low dark counting rate. They allow one to attain high collection efficiency with simple optical systems. However, they work at high bias voltage (over 200 V) with high power dissipation and are easily damaged by exposure to intense light. A detector carrier module has been designed for safe operation and full performance exploitation of any silicon device suitable for GM operation, with any breakdown voltage up to 480 V. Efficient photon counting and timing is achieved in a very compact module by means of an integrated active-quenching circuit (iAQC) with fast time pickup. Catastrophic failure is avoided by a dedicated monitor and safety circuit, even in the case of exposure to sunlight.
Journal of Modern Optics 01/2009; 56(Nos. 2–3):317-325. · 1.17 Impact Factor
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ABSTRACT: One of the main drawbacks of single-photon avalanche diode arrays is optical crosstalk between adjacent detectors. In the past, this phenomenon was basically ascribed to light propagating from one detector to another through a direct optical path. Accordingly, deep trenches coated with metal were introduced as optical isolation barriers between pixels. This solution, however, was unable to completely prevent the crosstalk. In this letter, we demonstrate that a strong contribution to optical crosstalk comes from photons reflected at the bottom of the chip. These photons can bypass trenches making them less effective.
IEEE Photonics Technology Letters 04/2008; · 2.19 Impact Factor
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ABSTRACT: A synchrotron light detector using a Single-Photon Avalanche Detector (SPAD) is planned for the LHC longitudinal diagnostics monitor, an application which requires high count rate, low noise and good time resolution. SPAD detectors have been developed at Milan Polytechnic with active quenching circuits. Initial tests of these detectors and currently available commercial timeto- digital data acquisition equipment were made at the ESRF. We present the results of those tests, an estimation of the performance that can be expected for the LHC case and an analysis of the difficulties, constraints and potential of this type of detector.
