Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., & Gol'tsman, G. N. (2010). Microwave-assisted슠measurement슠of the슠frequency슠response슠of슠terahertz슠HEB슠mixers슠with a슠fourier슠transform슠spectrometer. In 21st International Symposium on Space Terahertz Technology (pp. 420–423).
Abstract: We describe a novel method of operation of the HEB direct detector for use with a Fourier Transform Spectrometer. Instead of elevating the bath temperature, we have measured the RF response of waveguide HEB mixers by applying microwave radiation to select appropriate bias conditions. In our experiment, a microwave signal is injected into the HEB mixer via its IF port. By choosing an appropriate injection level, the device can be operated close to the desired operating point. Furthermore, we have shown that both thermal biasing and microwave injection can reproduce the same spectral response of the HEB mixer. However, with the use of microwave injection, there is no need to wait for the mixer to reach thermal equilibrium, so characterisation can be done in less time. Also, the liquid helium consumption for our wet cryostat is also reduced. We have demonstrated that the signalto-noise ratio of the FTS measurements can be improved with microwave injection.
|
Shurakov, A., Tong, E., Blundell, R., & Gol'tsman, G. (2012). Microwave stabilization of HEB mixer by a microchip controller. In IEEE MTT-S international microwave symposium digest (pp. 1–3).
Abstract: The stability of a Hot Electron Bolometer (HEB) mixer can be improved by the use of microwave injection. In this article we report a refinement of this approach. We introduce a microchip controller to facilitate the implementation of the stabilization scheme, and demonstrate that the feedback loop effectively suppresses drifts in the HEB bias current, leading to an improvement in the receiver stability. The measured Allan time of the mixer's IF output power is increased to > 10 s.
|
Shurakov, A., Tong, C. - Y. E., Blundell, R., Kaurova, N., Voronov, B., & Gol'tsman, G. (2013). Microwave stabilization of a HEB mixer in a pulse-tube cryocooler. IEEE Trans. Appl. Supercond., 23(3), 1501504.
Abstract: We report the results of our study of the stability of an 800 GHz hot electron bolometer (HEB) mixer cooled with a pulse-tube cryocooler. Pulse-tube cryocoolers introduce temperature fluctuations as well as mechanical vibrations at a frequency of ~1 Hz, both of which can cause receiver gain fluctuations at that frequency. In our system, the motor of the cryocooler was separated from the cryostat to minimize mechanical vibrations, leaving thermal effects as the dominant source of the receiver gain fluctuations. We measured root mean square temperature variations of the 4 K stage of ~7 mK. The HEB mixer was pumped by a solid state local oscillator at 810 GHz. The root mean square current fluctuations at the low noise operating point (1.50 mV, 56.5 μA) were ~0.12 μA, and were predominantly due to thermal fluctuations. To stabilize the bias current, microwave radiation was injected to the HEB mixer. The injected power level was set by a proportional-integral-derivative controller, which completely compensates for the bias current oscillations induced by the pulse-tube cryocooler. Significant improvement in the Allan variance of the receiver output power was obtained, and an Allan time of 5 s was measured.
|
Baubert, J., Salez, M., Delorme, Y., Pons, P., Goltsman, G., Merkel, H., et al. (2003). Membrane-based HEB mixer for THz applications. In J. - C. Chiao, V. K. Varadan, & C. Cané (Eds.), Proc. SPIE (Vol. 5116, pp. 551–562). SPIE.
Abstract: We report in this paper a new concept for 2.7 THz superconducting Niobium nitride (NbN) Hot-Electron Bolometer mixer (HEB). The membrane process was developped for space telecommnunication applications a few years ago and the HEB mixer concept is now considered as the best choice for low-noise submillimeter-wave frequency heterodyne receivers. The idea is then to join these two technologies. The novel fabrication scheme is to fabricate a NbN HEB mixer on a 1 μm thick stress-less Si3N4/SiO2 membrane. This seems to present numerous improvements concerning : use at higher RF frequencies, power coupling efficiency, HEB mixer sensitivity, noise temperature, and space applications. This work is to be continued within the framework of an ESA TRP project, a 2.7 THz heterodyne camera with numerous applications including a SOFIA airborne receiver. This paper presents the whole fabrication process, the validation tests and preliminary results. Membrane-based HEB mixer theory is currently being investigated and further tests such as heterodyne and Fourier transform spectrometry measurement are planed shortly.
|
Zhang, W., Miao, W., Li, S. L., Zhou, K. M., Shi, S. C., Gao, J. R., et al. (2013). Measurement of the spectral response of spiral-antenna coupled superconducting hot electron bolometers. IEEE Trans. Appl. Supercond., 23(3), 2300804.
Abstract: Measured spectral response of spiral-antenna coupled superconducting hot electron bolometers (HEBs) often drops dramatically at frequencies that are still within the frequency range of interest (e.g., ~ 5 THz). This is inconsistent with the implied low receiver noise temperatures from the same measurements. To understand this discrepancy, we exhaustively test and calibrate the thermal sources used in Fourier transform spectrometer measurements. We first investigate the absolute emission spectrum of high-pressure Hg arc lamp, then measure the spectral response of two spiral-antenna coupled NbN HEBs with a Martin-Puplett interferometer as spectrometer and 77 K blackbody as broadband signal source. The measured absolute emission spectrum of Hg arc lamp is proportional to frequency, corresponding to an equivalent blackbody temperature of 4000 K at 1 THz, 1500 K at 3 THz, and 800 K at 5 THz, respectively. Measured spectral response of spiral-antenna coupled NbN HEBs, corrected for air absorption, is nearly flat in the frequency range of 0.5-4 THz, consistent with simulated coupling efficiency between HEB and spiral-antenna. These results explain the discrepancy, and prove that spiral-antenna coupled superconducting NbN HEBs work well in a wide frequency range. In addition, this calibration method and these results are broadly applicable to other quasi-optical THz receivers.
|
