We report on the investigation of optimal bias region of a wide-band superconducting hot electron bolometer (HEB) mixer in terms of noise temperature performance for multi-pixel heterodyne receiver application in the 5-meter Dome A Terahertz Explorer (DATE5) telescope. By evaluating the double sideband (DSB) receiver noise temperature (T rec) across a wide frequency range from 0.2 THz to 1.34 THz and with a large number of bias points, a broad optimal bias region has been observed, illustrating a good bias applicability for multipixel application since the performance of the HEB mixer is uniquely determined by each bias point. The noise temperature of the HEB mixer has been analyzed by calibrating the noise contribution of all RF components, whose transmissions have been measured by a time-domain spectroscopy. The corrected noise temperature distribution shows a frequency independence relation. The dependence of the optimal bias region on the bath temperature of the HEB mixer has also been investigated, the bath temperature has limited effect on the lowest receiver noise temperature until 7 K, however the optimal bias region deteriorates obviously with increasing bath temperature.
In this article, we measure the double sideband (DSB) receiver noise temperature (
TrecDSB)of an NbN hot electron bolometer (HEB) mixer at three local oscillator frequencies of 1.6, 2.5, and 5.3 THz. The HEB has cleaned contact interfaces with a 200-nm-thick Au layer. The measured
TrecDSBvalues are 530 ± 11 K, 640 ± 18 K, and 2190 ±150 K at 1.6, 2.5, and 5.3 THz, respectively, using an air setup with total optical losses of 2.60 ± 0.04, 2.63 ± 0.16, and 4.70 ± 0.24 dB, respectively. We derived low mixer noise temperatures (
TmixerDSB)of 240 ± 6 K at 1.6 THz and 290 ± 13 K at 2.5 THz, achieving over 30% improvement compared to published NbN HEB mixers. This enhancement can reduce the integration time of a heterodyne instrument by roughly a factor of 2. At 5.3 THz,
TmixerDSBis 620 ± 55 K, showing limited improvement due to nonoptimized antenna geometry. These results also contribute to understanding the device physics of a wide HEB (4 μm) at high frequencies. The mixer was developed for the proposed Orbiting Astronomical Satellite for Investigating Stellar Systems and Single Aperture Large Telescope for Universe Studies (concept) missions.
Nb hot-electron bolometers (HEBs) with critical temperature T. = 5 to 6 K have previously demonstrated good heterodyne mixing performance at THz frequencies. HEBs with a lower critical temperature are predicted to have improved performance with lower noise. We present microwave (30GHz) mixing measurements on Nb HEB mixers with T, between 1.4 and 5.3 K. The reduced T, is obtained by application of a magnetic field, or by use of a bi-layer microbridge of Nb and Au with 'F e = 1.6 K. The mixer output noise and voltage range of low mixer noise are observed to decrease approximately linearly with reduction of T. The Nb-Au mixer has a mixer noise temperature TM = 50K (DSB) with reasonable dynamic range, and thus is promising for future single pixel and array receivers for THz spectroscopy.
Three observation bands are planned for the Dome A Terahertz Explorer (DATE5), with the superconducting hot-electron bolometer (HEB) served as the mixer for the H200 band ( 200 μm wavelength). In this paper, the performance of a twin-slot antenna coupled superconducting NbN HEB mixer is fully characterized at 1.34 THz. The measured uncorrected receiver noise temperature is 500 K and the intermediate frequency (IF) noise bandwidth is about 3 GHz. Moreover, the receiver stability is characterized by measuring the Allan variance time.
We report the measured sensitivities of a superconducting NbN hot electron bolometer (HEB) heterodyne receiver at 5.25 THz. Terahertz (THz) radiation is quasioptically coupled to a HEB mixer with a lens and a spiral antenna. Using a measurement setup with black body calibration sources and a beam splitter in vacuo, and an antireflection coated Si lens, we obtained a double sideband (DSB) receiver noise temperature (TrecDSB) of 1150 K, which is nine times hν/2k, where h is the Planck constant, ν the frequency, and k the Boltzmann constant. In addition, the measured far field beam patterns of the integrated lens antenna show nearly collimated beams from 2.5 to 5.3 THz that allow reliable measurement of TrecDSB using the vacuum setup. Our experimental results in combination with an antenna-to-bolometer coupling simulation suggest that the HEB mixer can work well at least up to 6 THz, making it suitable for next generation of high-resolution spectroscopic space telescopes and, in particular, for the detection of the neutral atomic oxygen line at 4.7 THz.
We report the measured sensitivities of a superconducting NbN hot electron bolometer (HEB) heterodyne receiver at 5.25 THz. The terahertz (THz) radiation is quasioptically coupled to the HEB mixer with a lens and a spiral antenna. Using a measurement setup with black body calibration sources and a beam splitter in vacuum, and an antireflection coated Si lens, we obtained a double sideband (DSB) receiver noise temperature ( ) of 1150 K, which is 4.5 times h/k (the quantum limit). In addition, the measured far field beam patterns of the integrated lens antenna from 2.5 THz to 5.3 THz show collimated beams that make it reliable to measure using the vacuum setup. Our experimental results in combination with an antenna-to-bolometer coupling simulation suggest that the HEB mixer can work well at least up to 6 THz, suitable for next generation of high-resolution spectroscopic space telescopes and, in particular, for the detection of the neutral atomic oxygen (OI) line at 4.7 THz. DSB rec T
China is now building an astronomical observatory including a THz telescope at Dome A on the Antarctic plateau. The development of superconducting HEB (Hot Electron Bolometer) mixers, the best choice for coherent detection at frequencies beyond 1 THz, becomes increasingly crucial. We present in this manuscript the investigation of high-sensitivity superconducting HEB mixers using quasi-optical technology in the THz region. The main results of this study are as follows: 1. We measured the dielectric constant of high-resistivity silicon at 77 K and 295 K by a vector measurement system. The measured permittivity is adopted to simulate the far-field beam pattern of a quasi-optical superconducting HEB mixer. 2. We measured the far-field beam pattern of a superconducting HEB mixer by both near-field heterodyne measurement system and far-field direct detection measurement system. The measured results accord well with the simulation. We also investigated the effect of HEB bias voltages and bath temperature on the far-field beam-pattern. 3. We successfully developed a high-sensitivity superconducting HEB mixer at 1.3 THz. The uncorrected measured double-sideband noise temperature is 600 K, which is a state-of-the-art result at this frequency. We systematically characterized heterodyne performances such as RF noise, conversion gain and noise bandwidth. We also measured the frequency response and calibrated it with a new method. Furthermore, we investigated the performance of this superconducting HEB mixer integrated with different elliptical lenses. 4. Finally, we measured the noise performance and the frequency response of a HEB mixer coupled to a 0.1-1.5 THz spiral antenna, the frequency dependence of the noise temperature has also been characterized. This study has provided a further understanding of superconducting HEB mixers and allowed the realization of a HEB mixer with state-of-the-art sensitivity at 1.3 THz. Hence the results of this study can find good use in the 5 m terahertz telescope (DATE5) at Dome A.