|
|
Zwiller V, Aichele T, Seifert W, Persson J, Benson O. Generating visible single photons on demand with single InP quantum dots. Appl Phys Lett. 2003;82(10):1509–11.
|
|
|
|
Finkel M, Vachtomin Y, Antipov S, Drakinski V, Kaurova N, Voronov B, et al. Gain bandwidth and noise temperature of NbTiN HEB mixer. In: Proc. 14th Int. Symp. Space Terahertz Technol.; 2003. p. 276–85.
Abstract: We have determined that the gain bandwidth of phonon-cooled HEB mixer employing NbTiN films deposited on MgO layer over Si substrate is limited b y the escape of phonons to the substrate. The cut-off frequencies of 1 um long devices operating at T 71, based on 3.5 nm. 4 nm and 10 nm thick films amount to 400 Mk. 300 MHz, and 100 MHz, respectivel y . The gain bandwidth of 0.13 . um long devices fabricated from 3.5 nm thick film is larger and amounts to 0.8 GIL; at the optimal operating point and to 1.5 GIL: at larger bias. The increase of the gain bandwidth from 400 MHz up to 1.5 GH: with the change of bridge length is attributed to diffusion cooling. A double sideband noise temperature of 4000 K was obtained for heterodyne receiver utilizing pilot NbTiN HEB mixer (not optimized for normal state resistance) operating at the local oscillator frequency of 2.5 THz.
|
|
|
|
Semenov A, Engel A, Il'in K, Gol'tsman G, Siegel M, Hübers H-W. Ultimate performance of a superconducting quantum detector. Eur Phys J Appl Phys. 2003;21(3):171–8.
Abstract: We analyze the ultimate performance of a superconducting quantum detector in order to meet requirements for applications in near-infrared astronomy and X-ray spectroscopy. The detector exploits a combined detection mechanism, in which avalanche quasiparticle multiplication and the supercurrent jointly produce a voltage response to a single absorbed photon via successive formation of a photon-induced and a current-induced normal hotspot in a narrow superconducting strip. The response time of the detector should increase with the photon energy providing energy resolution. Depending on the superconducting material and operation conditions, the cut-off wavelength for the single-photon detection regime varies from infrared waves to visible light. We simulated the performance of the background-limited infrared direct detector and X-ray photon counter utilizing the above mechanism. Low dark count rate and intrinsic low-frequency cut-off allow for realizing a background limited noise equivalent power of 10−20 W Hz−1/2 for a far-infrared direct detector exposed to 4-K background radiation. At low temperatures, the intrinsic response time of the counter is rather determined by diffusion of nonequilibrium electrons than by the rate of energy transfer to phonons. Therefore, thermal fluctuations do not hamper energy resolution of the X-ray photon counter that should be better than 10−3 for 6-keV photons. Comparison of new data obtained with a Nb based detector and previously reported results on NbN quantum detectors support our estimates of ultimate detector performance.
|
|
|
|
Verevkin A, Slysz W, Pearlman A, Zhang J, Sobolewski R, Okunev O, et al. Real-time GHz-rate counting of infrared photons using nanostructured NbN superconducting detectors. In: CLEO/QELS. Optical Society of America; 2003. CThM8.
Abstract: We demonstrate that our ultrathin, nanometer-width NbN superconducting single-photon detectors are capable of above 1-GHz-frequency, real-time counting of near-infrared photons. The measured system jitter of the detector is below 15 ps.
|
|
|
|
Myasnikova SE, Parshin VV, van't Klooster K, Valsecchi G. Reflectivity of antenna and mirrors reflectors at 110 and 200 GHz. In: Proc. 4th international conference on antenna theory and techniques. Vol 2.; 2003. p. 624–7.
Abstract: Reflectivity (reflection loss) investigations of nickel samples with different types of surface finish, with and without rhodium coating, have been carried out in the 110-200 GHz frequency range on an installation developed in the Applied Physics Institute of Russia. The reflectivity measurements of high quality silver coated and gold coated mirrors are also presented. The reflectivity (reflection loss) investigations of some carbon fibre samples with and without aluminium coating have been made. Results are interesting, in view of the anisotropy of the carbon fibre material.
|
|
|
|
van't Klooster CGM, Parshin VV, Myasnikova SE. Reflectivity of antenna reflectors: measurements at frequencies between 110 and 200 GHz. In: Proc. Antennas and propagation society international symposium. Vol 3.; 2003. p. 528–31.
Abstract: It is imperative to test the mechanical, electrical and thermal-optical properties of MM and sub-MM reflector antennas. Electrical, thermal and optical properties are very important and high-accurate measurements lead, obviously, to more accurate results in applications. This paper deals with measurement of electrical reflectivity in the range 110-200 GHz. Reflectivity has been measured for a number of samples, which represent materials used in reflector antennas. Both metal samples and carbon-fibre samples were tested in a dedicated facility available for this purpose at the Applied Physics Institute in Nizhny Novgorod (IAP). The test facility is shortly discussed, with techniques for data extraction. Calibration is done with high quality silver coated mirrors and aluminium control samples. Accurate results have been derived with indicative interesting results.
|
|
|
|
Hirata A, Harada M, Nagatsuma T. 120-GHz wireless link using photonic techniques for generation, modulation, and emission of millimeter-wave signals. J. of Lightwave Technology. 2003;21(10):2145–53.
Abstract: We present a wireless link system that uses millimeter-wave (MMW) photonic techniques. The photonic transmitter in the wireless link consists of an optical 120-GHz MMW generator, an optical modulator, and a high-power photonic MMW emitter. A uni-traveling carrier photodiode (UTC-PD) was used as the photonic emitter in order to eliminate electronic MMW amplifiers. We evaluated the dependence of UTC-PD output power on its transit-time limited bandwidth and its CR-time constant limited bandwidth, and employed a UTC-PD with the highest output power for the photonic emitter. As for the MMW generation, we developed a 120-GHz optical MMW generator that generates a pulse train and one that generates a sinusoidal signal. The UTC-PD output power generated by a narrow pulse train was higher than that generated by sinusoidal signals under the same average optical power condition, which contributes to reducing the photocurrent of the photonic emitter. We have experimentally demonstrated that the photonic transmitter can transmit data at up to 3.0 Gb/s. The wireless link using the photonic transmitter can be applied to optical gigabit Ethernet signals.
|
|
|
|
Khosropanah P. NbN and NbTiN hot electron bolometer THz mixers [Ph.D. thesis]. Göteborg: Chalmers University of Technology; 2003.
Abstract: The thesis reports the development of Hot Electron Bolometer (HEB) mixers for radio astronomy heterodyne receivers in THz frequency range. Part of this work is the fabrication of HEB devices, which are based on NbN or NbTiN superconducting thin films (â‰<a4>5 nm). They are integrated with wideband spiral or double-slot planar antennas. The mixer chips are incorporated into a quasi-optical receiver. The experimental part of this work focuses on the characterization of the receiver as a whole, and the HEB mixers as a part. Double side band receiver noise temperature and the IF bandwidth are reported for frequencies from 0.7 THz up to 2.6 THz. The spectrum of the direct response of HEB integrated with dierent antennas are measured using Fourier Transform Spectrometer (FTS). The effect of the bolometer size on total receiver performance and the LO power requirements is also discussed. A high-yield and reliable process for fabrication of NbN HEB mixers have been achieved. Over 100 devices with different bolometer geometry, film property and also different antennas have been fabricated and measured. The measured data enables us to discuss the impact of different parameters to the receiver overall performance.
This work has provided NbN HEB mixers to the following receivers:
TREND (Terahertz REceiver with NbN HEB Device) operating at 1.25-1.5 THz, installed in AST/RO Submillimeter Wave Telescope, Amundsen/Scott South Pole Station, in 2002-2003.
Band 6-low (1.410-1.700 THz) and 6-high (1.700-1.920 THz) of the HIFI (Heterodyne Instrument for Far Infra-red) in the Herschel Space Observatory, due to launch in 2007 by ESA (European Space Agency).
Besides, there has been continuous efforts to develop better models to explain the mixer performance more accurately. They are based on two temperature model for electrons and phonons and solving one-dimensional heat balance equations along the bolometer. The principles of these models are illustrated and the calculated results are compared with measured data.
Keywords: HEB mixer, hot electron bolometer mixer, NbN, NbTiN, superconducting detector, heterodyne receiver, THz mixer, submillimeter mixer, quasioptical receiver, double slot antenna, twin slot antenna, spiral antenna, receiver noise, FTS, Fourier Transform Spectrometer
|
|
|
|
Tinkham M, Free JU, Lau CN, Markovic N. Hysteretic I–V curves of superconducting nanowires. Phys. Rev. B. 2003;68:134515(1 to 7).
Abstract: Experimental I–V curves of superconducting MoGe nanowires show hysteresis for the thicker wires and none for the thinner wires. A rather quantitative account of these data for representative wires is obtained by numerically solving the one-dimensional heat flow equation to find a self-consistent distribution of temperature and local resistivity along the wire, using the measured linear resistance R(T) as input. This suggests that the retrapping current in the hysteretic I–V curves is primarily determined by heating effects, and not by the dynamics of phase motion in a tilted washboard potential as often assumed. Heating effects and thermal fluctuations from the low-resistance state to a high-resistance, quasinormal regime appear to set independent upper bounds for the switching current.
|
|
|
|
Anthore A, Pothier H, Esteve D. Density of states in a superconductor carrying a supercurrent. Phys Rev Lett. 2003;90(12):127001 (1 to 4).
Abstract: We have measured the tunneling density of states (DOS) in a superconductor carrying a supercurrent or exposed to an external magnetic field. The pair correlations are weakened by the supercurrent, leading to a modification of the DOS and to a reduction of the gap. As predicted by the theory of superconductivity in diffusive metals, we find that this effect is similar to that of an external magnetic field.
|
|
