Ryabchun, S., Tong, C. - Y. E., Blundell, R., Kimberk, R., & Gol'tsman, G. (2007). Study of the effect of microwave radiation on the operation of HEB mixers in the terahertz frequency range. IEEE Trans. Appl. Supercond., 17(2), 391–394.
Abstract: We have investigated the effect of injecting microwave radiation, with a frequency much lower than that corresponding to the energy gap of the superconductor, on the performance of the hot-electron bolometer mixer incorporated into a THz heterodyne receiver. More specifically, we show that exposing the mixer to microwave radiation does not cause a significant rise of the receiver noise temperature and fall of the mixer conversion gain so long as the microwave power is a small fraction of local oscillator power. The injection of a small, but controlled amount of microwave power therefore enables active compensation of local oscillator power and coupling fluctuations which can significantly degrade the gain stability of hot electron bolometer mixer receivers.
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Dauler, E. A., Robinson, B. S., Kerman, A. J., Yang, J. K. W., Rosfjord, E. K. M., Anant, V., et al. (2007). Multi-element superconducting nanowire single-photon detector. IEEE Trans. Appl. Supercond., 17(2), 279–284.
Abstract: A multi-element superconducting nanowire single photon detector (MESNSPD) is presented that consists of multiple independently-biased superconducting nanowire single photon detector (SNSPD) elements that form a continuous active area. A two-element SNSPD has been fabricated and tested, showing no measurable crosstalk between the elements, sub-50-ps relative timing jitter, and four times the maximum counting rate of a single SNSPD with the same active area. The MESNSPD can have a larger active area and higher speed than a single-element SNSPD and the input optics can be designed so that the detector provides spatial, spectral or photon number resolution.
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Jiang, L., Antipov, S. V., Voronov, B. M., Gol'tsman, G. N., Zhang, W., Li, N., et al. (2007). Characterization of the performance of a quasi-optical NbN superconducting HEB mixer. IEEE Trans. Appl. Supercond., 17(2), 395–398.
Abstract: In this paper we focus mainly on the investigation of the performance of a quasi-optical (planar log-spiral antenna) phonon-cooled NbN superconducting hot electron bolometer (HEB) mixer, which is cryogenically cooled by a close-cycled 4-K cryocooler, at 500 and 850 GHz frequency bands. The mixer's noise performance, stability of IF output power, and local oscillator (LO) power requirement are characterized for three NbN superconducting HEB devices of different sizes. The transmission characteristics of Mylar and Zitex films with incidence waves of an elliptical polarization are also examined by measuring the mixer's noise temperature. The lowest receiver noise temperatures (with no corrections) of 750 and 1100 K are measured at 500 and 850 GHz, respectively. Experimental results also demonstrate that the bigger the HEB device is, the higher the stability of IF output power becomes.
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Zhang, W., Li, N., Jiang, L., Miao, W., Lin, Z. - H., Yao, Q. - J., et al. (2007). Noise behaviour of a THz superconducting hot-electron bolometer mixer. Chinese Phys. Lett., 24(6), 1778–1781.
Abstract: A quasi-optical superconducting NbN hot-electron bolometer (HEB) mixer is measured in the frequency range of 0.5–2.5 THz for understanding of the frequency dependence of noise temperature of THz coherent detectors. It has been found that noise temperature increasing with frequency is mainly due to the coupling loss between the quasi-optical planar antenna and the superconducting HEB bridge when taking account of non-uniform distribution of high-frequency current. With the coupling loss corrected, the superconducting HEB mixer demonstrates a noise temperature nearly independent of frequency.
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Maslennikov, S. N., Finkel, M. I., Antipov, S. V., Polyakov, S. L., Zhang, W., Ozhegov, R., et al. (2006). Spiral antenna coupled and directly coupled NbN HEB mixers in the frequency range from 1 to 70 THz. In Proc. 17th Int. Symp. Space Terahertz Technol. (pp. 177–179). Paris, France.
Abstract: We investigate both antenna coupled and directly coupled HEB mixers at several LO frequencies within the range of 2.5 THz to 70 THz. H20 (2.5+10.7 THz), and CO2 (30 THz) gas discharge lasers are used as the local oscillators. The noise temperature of antenna coupled mixers is measured at LO frequencies of 2.5 THz, 3.8 THz, and 30 THz. The results for both antenna coupled and directly coupled mixer types are compared. The devices with in—plane dimensions of 5x5 ,um 2 are pumped by LO radiation at 10.7 THz. The directly coupled HEB demonstrates nearly flat dependence of responsivity on frequency in the range of 25+64 THz.
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