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Kovalyuk V, Hartmann W, Kahl O, Kaurova N, Korneev A, Goltsman G, et al. Absorption engineering of NbN nanowires deposited on silicon nitride nanophotonic circuits. Opt Express. 2013;21(19):22683–92.
Abstract: We investigate the absorption properties of U-shaped niobium nitride (NbN) nanowires atop nanophotonic circuits. Nanowires as narrow as 20nm are realized in direct contact with Si3N4 waveguides and their absorption properties are extracted through balanced measurements. We perform a full characterization of the absorption coefficient in dependence of length, width and separation of the fabricated nanowires, as well as for waveguides with different cross-section and etch depth. Our results show excellent agreement with finite-element analysis simulations for all considered parameters. The experimental data thus allows for optimizing absorption properties of emerging single-photon detectors co-integrated with telecom wavelength optical circuits.
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Schuck C, Pernice WHP, Minaeva O, Li M, Gol'tsman G, Sergienko AV, et al. Matrix of integrated superconducting single-photon detectors with high timing resolution. IEEE Trans Appl Supercond. 2013;23(3):2201007.
Abstract: We demonstrate a large grid of individually addressable superconducting single photon detectors on a single chip. Each detector element is fully integrated into an independent waveguide circuit with custom functionality at telecom wavelengths. High device density is achieved by fabricating the nanowire detectors in traveling wave geometry directly on top of silicon-on-insulator waveguides. Our superconducting single photon detector matrix includes detector designs optimized for high detection efficiency, low dark count rate, and high timing accuracy. As an example, we exploit the high timing resolution of a particularly short nanowire design to resolve individual photon round-trips in a cavity ring-down measurement of a silicon ring resonator.
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Trifonov A, Tong C-YE, Blundell R, Ryabchun S, Gol'tsman G. Probing the stability of HEB mixers with microwave injection. IEEE Trans Appl Supercond. 2015;25(3):2300404 (1 to 4).
Abstract: Using a microwave probe as a tool, we have performed experiments aimed at understanding the origin of the output-power fluctuations in hot-electron-bolometer (HEB) mixers. We use a probe frequency of 1.5 GHz. The microwave probe picks up impedance changes of the HEB, which are examined upon demodulation of the reflected wave outside the cryostat. This study shows that the HEB mixer operates in two different regimes under a terahertz pump. At a low pumping level, strong pulse modulation is observed, as the device switches between the superconducting state and the normal state at a rate of a few megahertz. When pumped much harder, to approximate the low-noise mixer operating point, residual modulation can still be observed, showing that the HEB mixer is intrinsically unstable even in the resistive state. Based on these observations, we introduced a low-frequency termination to the HEB mixer. By terminating the device in a 50-Ω resistor in the megahertz frequency range, we have been able to improve the output-power Allan time of our HEB receiver by a factor of four to about 10 s for a detection bandwidth of 15 MHz, with a corresponding gain fluctuation of about 0.035%.
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Maslennikov S. RF heating efficiency of the terahertz superconducting hot-electron bolometer. arXiv [Internet]. 2014 [cited 2024 Jul 7];1404.5276:1–4;arXiv:1404.5276. Available from: http://arxiv.org/abs/1404.5276
Abstract: We report results of the numerical solution by the Euler method of the system of heat balance equations written in recurrent form for the superconducting hot-electron bolometer (HEB) embedded in an electrical circuit. By taking into account the dependence of the HEB resistance on the transport current we have been able to calculate rigorously the RF heating efficiency, absorbed local oscillator (LO) power and conversion gain of the HEB mixer. We show that the calculated conversion gai nis in excellent agreement with the experimental results, and that the substitution of the calculated RF heating efficiency and absorbed LO power into the expressions for the conversion gain and noise temperature given by the analytical small-signal model of the HEB yields excellent agreement with the corresponding measured values
Keywords: superconducting hot-electron bolometer mixer, HEB, NbN, distributed model, HEB model, HEB mixer model, heat balance equa-tions, conversion gain, RF heating efficiency, noise temperature, simulation, Euler method
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Gol’tsman G, Okunev O, Chulkova G, Lipatov A, Dzardanov A, Smirnov K, et al. Fabrication and properties of an ultrafast NbN hot-electron single-photon detector. IEEE Trans Appl Supercond. 2001;11(1):574–7.
Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film’s supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.
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Zhang W, Miao W, Zhong JQ, Shi SC, Hayton DJ, Vercruyssen N, et al. Temperature dependence of the receiver noise temperature and IF bandwidth of superconducting hot electron bolometer mixers. Supercond Sci Technol. 2014;27(8):085013 (1 to 5).
Abstract: In this paper we study the temperature dependence of the receiver noise temperature and IF noise bandwidth of superconducting hot electron bolometer (HEB) mixers. Three superconducting NbN HEB devices of different transition temperatures (Tc) are measured at 0.85 THz and 1.4 THz at different bath temperatures (Tbath) between 4 K and 9 K. Measurement results demonstrate that the receiver noise temperature of superconducting NbN HEB devices is nearly constant for Tbath/Tc, less than 0.8, which is consistent with the simulation based on a distributed hot-spot model. In addition, the IF noise bandwidth appears independent of Tbath/Tc, indicating the dominance of phonon cooling in the investigated HEB devices.
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Zhang W, Miao W, Yao QJ, Lin ZH, Shi SC, Gao JR, et al. Spectral response and noise temperature of a 2.5 THz spiral antenna coupled NbN HEB mixer. Phys Procedia. 2012;36:334–7.
Abstract: We report on a 2.5 THz spiral antenna coupled NbN hot electron bolometer (HEB) mixers, fabricated with in-situ process. The receiver noise temperature with lowest value of 1180 K is in good agreement with calculated quantum efficiency factor as a function of bias voltage. In addition, the measured spectral response of the spiral antenna coupled NbN HEB mixer shows broad frequency coverage of 0.8-3 THz, and corrected response for optical losses, FTS, and coupling efficiency between antenna and bolometer falls with frequency due to diffraction-limited beam of lens/antenna combination.
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Beck M, Rousseau I, Klammer M, Leiderer P, Mittendorff M, Winnerl S, et al. Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses. Phys Rev Lett. 2013;110(26):267003 (1 to 5).
Abstract: Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Delta/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Delta/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.
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Pentin IV, Smirnov AV, Ryabchun SA, Ozhegov RV, Gol’tsman GN, Vaks VL, et al. Semiconducting superlattice as a solid-state terahertz local oscillator for NbN hot-electron bolometer mixers. Tech Phys. 2012;57(7):971–4.
Abstract: We present the results of our studies of the semiconducting superlattice (SSL) frequency multiplier and its application as part of the solid state local oscillator (LO) in the terahertz heterodyne receiver based on a NbN hot-electron bolometer (HEB) mixer. We show that the SSL output power level increases as the ambient temperature is lowered to 4.2 K, the standard HEB operation temperature.
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Gurovich BA, Tarkhov MA, Prikhod'ko KE, Kuleshova EA, Komarov DA, Stolyarov VL, et al. Controlled modification of superconducting properties of NbN ultrathin films under composite ion beam irradiation. Nanotechnologies in Russia. 2014;9(7):386–90.
Abstract: In this work, the results of studying the microstructure and superconducting properties of ultrathin films on the basis of NbN in the initial state and after modification by being subjecting to composite ion beam irradiation with the energy ~1–3) keV are presented. HRTEM analysis showed that the initial films on the sapphire substrate in orientation “c-cut†are characterized by a grain size essentially exceeding the film thickness, while on the other substrates the size of grains corresponds to the thickness of film. Using XPS analysis, it was shown that in the initial films the atomic ratio of Nb and N is 0.51/0.49, respectively, the percentage of oxygen being lower than 5%. For ultrathin films 5 nm in thickness, the critical temperature of transit to superconducting state (T c) is found to be ~3.6 K and the density of critical current is jc ~8MA/cm2. In the work it is experimentally determined that the irradiation of NbN films by composite ion beams leads to the controlled modification of its superconducting properties due to the process of selective substitution of nitrogen atoms on the oxygen atoms.
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