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Author Lee, B. G.; Assefa, S.; Green, W. M. J.; Min Yang; Schow, C. L.; Jahnes, C. V.; Sheng Zhang; Singer, J.; Kopp, V. I.; Kash, J. A.; Vlasov, Y. A.
Title Multichannel high-bandwidth coupling of ultradense silicon photonic waveguide array to standard-pitch fiber array Type Journal Article
Year 2011 Publication J. Lightwave Technol. Abbreviated Journal
Volume 29 Issue (down) 4 Pages 475-482
Keywords optical waveguides, from chiralphotonics
Abstract A multichannel tapered coupler interfacing standard 250-μm-pitch low-numerical-aperture (NA) polarization-maintaining fiber arrays with ultradense 20- μm-pitch high-NA silicon waveguides is designed and fabricated. The coupler is based on an array of 12 dual-core glass waveguides on 250-μ m pitch that are tapered to a 20- μm pitch, simultaneously providing both pitch and spot-size conversion. At the wide end, the inner core matches the NA and mode profile of standard single-mode fiber. When drawn and tapered, the inner core “vanishes” and the outer core, surrounded by the clad, matches the NA and mode profile of the on-chip photonic waveguide. Ultradense high-efficiency coupling to an array of Si photonic waveguides is demonstrated using a 12-channel polarization-maintaining-fiber pigtailed tapered coupler. Coupling to Si waveguides is facilitated using SiON spot-size converters integrated into the Si photonic IC to provide 2-3-μm mode field diameters compatible with the tapered coupler. The tapered coupler achieves <; 1 dB coupling losses to photonic waveguides. Furthermore, eight-channel coupling is shown with less than -35 dB crosstalk between channels. Finally, a 640-Gb/s wavelength-division-multiplexing signal is coupled into four waveguides occupying 80 μm of chip edge, providing 160-Gb/s per-channel bandwidths.
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Call Number Serial 849
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Author Korneeva, Y.; Florya, I.; Semenov, A.; Korneev, A.; Goltsman, G.
Title New generation of nanowire NbN superconducting single-photon detector for mid-infrared Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal IEEE Trans. Appl. Supercond.
Volume 21 Issue (down) 3 Pages 323-326
Keywords SSPD
Abstract We present a break-through approach to mid-infrared single-photon detection based on nanowire NbN superconducting single-photon detectors (SSPD). Although SSPD became a mature technology for telecom wavelengths (1.3-1.55 μm) its further expansion to mid-infrared wavelength was hampered by low sensitivity above 2 μm. We managed to overcome this limit by reducing the nanowire width to 50 nm, while retaining high superconducting properties and connecting the wires in parallel to produce a voltage response of sufficient magnitude. The new device exhibits 10 times better quantum efficiency at 3.5 μm wavelength than the “standard” SSPD.
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Call Number RPLAB @ gujma @ Serial 644
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Author Ozhegov, R. V.; Gorshkov, K. N.; Gol'tsman, G. N.; Kinev, N. V.; Koshelets, V. P.
Title The stability of a terahertz receiver based on a superconducting integrated receiver Type Journal Article
Year 2011 Publication Supercond. Sci. Technol. Abbreviated Journal Supercond. Sci. Technol.
Volume 24 Issue (down) 3 Pages 035003
Keywords SIS mixer, SIR, stability
Abstract We present the results of stability testing of a terahertz radiometer based on a superconducting receiver with a SIS tunnel junction as the mixer and a flux-flow oscillator as the local oscillator. In the continuum mode, the receiver with a noise temperature of 95 K at 510 GHz measured over the intermediate frequency (IF) passband of 4-8 GHz offered a noise equivalent temperature difference of 10 ± 1 mK at an integration time of 1 s. We offer a method to significantly increase the integration time without the use of complex measurement equipment. The receiver observed a strong signal over a final detection bandwidth of 4 GHz and offered an Allan time of 5 s.
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Call Number RPLAB @ gujma @ Serial 705
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Author Tretyakov, Ivan; Ryabchun, Sergey; Finkel, Matvey; Maslennikov, Sergey; Maslennikova, Anna; Kaurova, Natalia; Lobastova, Anastasia; Voronov, Boris; Gol'tsman, Gregory
Title Ultrawide noise bandwidth of NbN hot-electron bolometer mixers with in situ gold contacts Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal
Volume 21 Issue (down) 3 Pages 620-623
Keywords NbN HEB mixer bandwidth
Abstract We report a noise bandwidth of 7 GHz in the new generation of NbN hot-electron bolometer (HEB) mixers that are being developed for the space observatory Millimetron. The HEB receiver driven by a 2.5-THz local oscillator offered a noise temperature of 600 K in a 50-MHz final detection bandwidth. As the filter center frequency was swept this value remained nearly constant up to the cutoff frequency of the cryogenic amplifier at 7 GHz. We believe that such a low value of the noise temperature is due to reduced radio frequency (RF) loss at the interface between the superconducting film and the gold contacts. We have also performed gain bandwidth measurements at the superconducting transition on HEB mixers with various lengths and found them to be in excellent agreement with the results of the analytical and numerical models developed for the HEB mixer with both diffusion and phonon cooling of hot electrons.
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Call Number RPLAB @ gujma @ Serial 716
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Author Lobanov, Y.; Tong, E.; Blundell, R.; Hedden, A.; Voronov, B.; Gol'tsman, G.
Title Large-signal frequency response of an HEB mixer: from 300 MHz to terahertz Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal
Volume 21 Issue (down) 3 Pages 628-631
Keywords waveguide NbN HEB mixers
Abstract We present a study of the large signal frequency response of an HEB mixer over a wide frequency range. In our experiments, we have subjected the HEB mixer to incident electromagnetic radiation from 0.3 GHz to 1 THz. The mixer element is an NbN film deposited on crystalline quartz. The mixer chip is mounted in a waveguide cavity, coupled to free space with a diagonal horn. At microwave frequencies, electromagnetic radiation is applied through the coaxial bias port of the mixer block. At higher frequencies the input signal passes via the diagonal horn feed. At each frequency, the incident power is varied and a family of I-V curves is recorded. From the curves we identify 3 distinct regimes of operation of the mixer separated by the phonon relaxation frequency and the superconducting energy gap frequency observed at about 3 GHz and 660 GHz respectively. In this paper, we will present observed curves and discuss the results of our experiment.
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Call Number RPLAB @ gujma @ Serial 719
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Author Lobanov, Y.V.; Tong, C.-Y.E.; Hedden, A.S.; Blundell, R.; Voronov, B.M.; Gol'tsman, G.N.
Title Direct measurement of the gain and noise bandwidths of HEB mixers Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal IEEE Trans. Appl. Supercond.
Volume 21 Issue (down) 3 Pages 645-648
Keywords waveguide NbN HEB mixers
Abstract The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.
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Call Number RPLAB @ gujma @ Serial 720
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Author Kawakami, A; Saito, S.; Hyodo, M.
Title Fabrication of nano-antennas for superconducting Infrared detectors Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal
Volume 21 Issue (down) 3 Pages 632-635
Keywords optical antennas, NbN/MgO/NbN/TiN/Al HEB, dipole antennas, IR, infrared
Abstract To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antenna's center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed.
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Call Number Serial 761
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Author Galeazzi, Massimiliano
Title Fundamental noise processes in TES devices Type Journal Article
Year 2011 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal IEEE Trans. Appl. Supercond.
Volume 21 Issue (down) 3 Pages 267-271
Keywords TES, Johnson noise, phonon noise, excess noise, flux-flow noise, thermal fluctuation noise
Abstract Microcalorimeters and bolometers are noise-limited devices, therefore, a proper understanding of all noise sources is essential to predict and interpret their performance. In this paper, I review the fundamental noise processes contributing to Transition Edge Sensor (TES) microcalorimeters and bolometers and their effect on device performance. In particular, I will start with a simple, monolithic device model, moving to a more complex one involving discrete components, to finally move to today's more realistic, comprehensive model. In addition to the basic noise contribution (equilibrium Johnson noise and phonon noise), TES are significantly affected by extra noise, which is commonly referred to as excess noise. Different fundamental processes have been proposed and investigated to explain the origin of this excess noise, in particular near equilibrium non-linear Johnson noise, flux-flow noise, and internal thermal fluctuation noise. Experimental evidence shows that all three processes are real and contribute, at different levels, to the TES noise, although different processes become important at different regimes. It is therefore time to discard the term “excess noise” and consider these terms part of the “fundamental noise processes” instead.
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Notes Recommended by Klapwijk Approved no
Call Number Serial 914
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Author Baek, Burm; Lita, Adriana E.; Verma, Varun; Nam, Sae Woo
Title Superconducting a-WxSi1–x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm Type Journal Article
Year 2011 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.
Volume 98 Issue (down) 25 Pages 3
Keywords SNSPD
Abstract We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1–x) nanowire. Our device made from a uniform a-WxSi1–x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates.
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Call Number RPLAB @ gujma @ Serial 665
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Author Peruzzo, Alberto; Laing, Anthony; Politi, Alberto; Rudolph, Terry; O'Brien, Jeremy L.
Title Multimode quantum interference of photons in multiport integrated devices Type Journal Article
Year 2011 Publication Nature Communications Abbreviated Journal Nat. Comm.
Volume 2 Issue (down) 224 Pages 6
Keywords fromIPMRAS
Abstract Photonics is a leading approach in realizing future quantum technologies and recently, optical waveguide circuits on silicon chips have demonstrated high levels of miniaturization and performance. Multimode interference (MMI) devices promise a straightforward implementation of compact and robust multiport circuits. Here, we show quantum interference in a 2×2 MMI coupler with visibility of V=95.6+/-0.9%. We further demonstrate the operation of a 4×4 port MMI device with photon pairs, which exhibits complex quantum interference behaviour. We have developed a new technique to fully characterize such multiport devices, which removes the need for phase-sensitive measurements and may find applications for a wide range of photonic devices. Our results show that MMI devices can operate in the quantum regime with high fidelity and promise substantial simplification and concatenation of photonic quantum circuits.
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Call Number RPLAB @ gujma @ Serial 763
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