Okunev O, Chulkova G, Milostnaya I, Antipov A, Smirnov K, Morozov D, et al. Registration of infrared single photons by a two-channel receiver based on fiber-coupled superconducting single-photon detectors. In: Sukhoivanov IA, Svich VA, Shmaliy YS, editors. Proc. SPIE. Vol 7009. SPIE; 2008. 70090V (1 to 8).
Abstract: Single-photon detectors (SPDs) are the foundation of all quantum communications (QC) protocols. Among different classes of SPDs currently studied, NbN superconducting SPDs (SSPDs) are established as the best devices for ultrafast counting of single photons in the infrared (IR) wavelength range. The SSPDs are nanostructured, 100 μm2 in total area, superconducting meanders, patterned by electron lithography in ultra-thin NbN films. Their operation has been explained within a phenomenological hot-electron photoresponse model. We present the design and performance of a novel, two-channel SPD receiver, based on two fiber-coupled NbN SSPDs. The receivers have been developed for fiber-based QC systems, operational at 1.3 μm and 1.55 μm telecommunication wavelengths. They operate in the temperature range from 4.2 K to 2 K, in which the NbN SSPDs exhibit their best performance. The receiver unit has been designed as a cryostat insert, placed inside a standard liquid-heliumstorage dewar. The input of the receiver consists of a pair of single-mode optical fibers, equipped with the standard FC connectors and kept at room temperature. Coupling between the SSPD and the fiber is achieved using a specially designed, precise micromechanical holder that places the fiber directly on top of the SSPD nanostructure. Our receivers achieve the quantum efficiency of up to 7% for near-IR photons, with the coupling efficiency of about 30%. The response time was measured to be < 1.5 ns and it was limited by our read-out electronics. The jitter of fiber-coupled SSPDs is < 35 ps and their dark-count rate is below 1s-1. The presented performance parameters show that our single-photon receivers are fully applicable for quantum correlation-type QC systems, including practical quantum cryptography.
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Korneev A, Minaeva O, Divochiy A, Antipov A, Kaurova N, Seleznev V, et al. Ultrafast and high quantum efficiency large-area superconducting single-photon detectors. In: Dusek M, Hillery MS, Schleich WP, Prochazka I, Migdall AL, Pauchard A, editors. Proc. SPIE. Vol 6583. Spie; 2007. 65830I (1 to 9).
Abstract: We present our latest generation of superconducting single-photon detectors (SSPDs) patterned from 4-nm-thick NbN films, as meander-shaped 0.5-mm-long and 100-nm-wide stripes. The SSPDs exhibit excellent performance parameters in the visible-to-near-infrared radiation wavelengths: quantum efficiency (QE) of our best devices approaches a saturation level of 30% even at 4.2 K (limited by the NbN film optical absorption) and dark counts as low as 2x10-4 Hz. The presented SSPDs were designed to maintain the QE of large-active-area devices, but, unless our earlier SSPDs, hampered by a significant kinetic inductance and a nanosecond response time, they are characterized by a low inductance and GHz counting rates. We have designed, simulated, and tested the structures consisting of several, connected in parallel, meander sections, each having a resistor connected in series. Such new, multi-element geometry led to a significant decrease of the device kinetic inductance without the decrease of its active area and QE. The presented improvement in the SSPD performance makes our detectors most attractive for high-speed quantum communications and quantum cryptography applications.
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Slysz W, Wegrzecki M, Bar J, Grabiec P, Gorska M, Rieger E, et al. Fiber-coupled NbN superconducting single-photon detectors for quantum correlation measurements. In: Dusek M, Hillery MS, Schleich WP, Prochazka I, Migdall AL, Pauchard A, editors. Proc. SPIE. Vol 6583. Spie; 2007. 65830J (1 to 11).
Abstract: We have fabricated fiber-coupled superconducting single-photon detectors (SSPDs), designed for quantum-correlationtype experiments. The SSPDs are nanostructured ( 100-nm wide and 4-nm thick) NbN superconducting meandering stripes, operated in the 2 to 4.2 K temperature range, and known for ultrafast and efficient detection of visible to nearinfrared photons with almost negligible dark counts. Our latest devices are pigtailed structures with coupling between the SSPD structure and a single-mode optical fiber achieved using a micromechanical photoresist ring placed directly over the meander. The above arrangement withstands repetitive thermal cycling between liquid helium and room temperature, and we can reach the coupling efficiency of up to 33%. The system quantum efficiency, measured as the ratio of the photons counted by SSPD to the total number of photons coupled into the fiber, in our early devices was found to be around 0.3 % and 1% for 1.55 &mgr;m and 0.9 &mgr;m photon wavelengths, respectively. The photon counting rate exceeded 250 MHz. The receiver with two SSPDs, each individually biased, was placed inside a transport, 60-liter liquid helium Dewar, assuring uninterrupted operation for over 2 months. Since the receiver’s optical and electrical connections are at room temperature, the set-up is suitable for any applications, where single-photon counting capability and fast count rates are desired. In our case, it was implemented for photon correlation experiments. The receiver response time, measured as a second-order photon cross-correlation function, was found to be below 400 ps, with timing jitter of less than 40 ps.
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Dauler EA, Kerman AJ, Robinson BS, Yang JKW, Voronov BM, Gol’tsman GN, et al. Achieving high counting rates in superconducting nanowire single-photon detectors. In: CLEO/QELS. Optical Society of America; 2006. JTuD3 (1 to 2).
Abstract: Kinetic inductance is determined to be the primary limitation to the counting rate of superconducting nanowire single-photon counters. Approaches for overcoming this limitation will be discussed.
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González FJ, Boreman GD. Comparison of dipole, bowtie, spiral and log-periodic IR antennas. Inf Phys & Technol. 2005;46(5):418–28.
Abstract: Antenna-coupled microbolometers use planar lithographic antennas to couple infrared radiation into a bolometer with sub-micron dimensions. In this paper four different types of infrared antennas were fabricated on thin grounded-substrates and coupled to microbolometers. Dipole, bowtie, spiral and log-periodic IR antenna-coupled detectors were measured at 10.6 μm and their performance compared. A new method to calculate the radiation efficiency based on the spatial and angular response of infrared antennas is presented and used to evaluate their performance. The calculated radiation efficiency for the dipole, bowtie, spiral and log-periodic IR antennas was 20%, 37%, 25% and 46% respectively. A dipole-length study was performed and shows that the quasistatic value of the effective permittivity accurately describes the incident wavelength in the substrate at infrared frequencies for antennas on a thin substrate.
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