Double Sideband Receiver Noise Temperature Research Articles

Heterodyne performance and characteristics of terahertz MgB2 hot electron bolometers

We have studied THz heterodyne detection in sub-micrometer MgB2 hot electron bolometer (HEB) mixers based on superconducting MgB2 films of ∼5nm (HEB-A), corresponding to a critical temperature (Tc) of 33.9 K, and ∼7nm (HEB-B), corresponding to a Tc of 38.4 K. We have measured a double sideband (DSB) receiver noise temperature of 2590 K for HEB-A and 2160 K for HEB-B at 1.6 THz and 5 K. By correcting for optical losses, both HEBs show receiver noise temperatures of ∼1600 K referenced to the front of anti-reflection (AR)-coated Si lenses. An intermediate frequency (IF) noise bandwidth of 11 GHz has been measured for both devices. The required local oscillator (LO) power is about 13 μW for both HEBs. We have also measured a DSB receiver noise temperature of 3290 K at 2.5 THz and 5 K but with an AR-coated lens optimized for 1.6 THz. Besides, we have observed a step-like structure in current voltage (IV) curves, which becomes weaker when the LO power increases and observable only in their differential resistance. Such a correlated structure appears also in the receiver output power as a function of voltage, which is likely due to electronic inhomogeneities intrinsic to the variations in the thickness of the MgB2 films. Different behavior in the IV curves around the low bias voltages, pumped with the same LO power at 1.6 and 5.3 THz, was observed for HEB-B, suggesting the presence of a high-energy σ-gap in the MgB2 film.

Low noise MgB2 hot electron bolometer mixer operated at 5.3 THz and at 20 K

We have demonstrated a low noise superconducting MgB2 hot electron bolometer (HEB) mixer working at the frequency of 5.3 terahertz (THz) with 20 K operation temperature. The bolometer consists of a 7 nm thick MgB2 submicrometer bridge contacted with a spiral antenna to couple THz radiation through a high resistive Si lens, and it has a superconducting critical temperature of 38 K. By using hot/cold blackbody loads and a Mylar beam splitter all in vacuum and applying a 5.25 THz far-infrared gas laser as a local oscillator, we measured a minimal double sideband receiver noise temperature of 3960 K at the LO power of 9.5 μW. This can be further reduced to 2920 K if a Si lens with an antireflection coating optimized at this frequency and a 3 μm beam splitter are used. The measured intermediate frequency (IF) noise bandwidth is 9.5 GHz. The low noise, wide IF bandwidth mixers, which can be operated in a compact, low dissipation Stirling cooler, are more suitable for space applications than the existing HEB mixers. Furthermore, we likely observed a signature of the double-gap in MgB2 by comparing current–voltage curves pumped at 5.3 and 1.6 THz.

The Influence of LO Power Heating of the Tunnel Junction on the Performance of THz SIS Mixers

We describe the performance of a superconductor- insulator-superconductor (SIS) mixer operating in the frequency range of 780-950 GHz. Unlike most SIS mixers, the tunnel junction employs two different superconductors, a niobium nitride top and a niobium bottom electrode sandwiching an aluminum nitride barrier layer, fabricated on a niobium titanium nitride ground plane. The mixer was tested in a pulse tube cryostat, with all the optical components, in the signal path, mounted inside the vacuum environment to avoid attenuation of the RF signal as it propagates from the hot/cold loads to the mixer. With this setup, we have measured an RF-corrected noise temperature of ~220 K. In this article, we focus on investigating the influence of local oscillator (LO) power heating on the performance of the terahertz mixer. The increase in the junction's physical temperature can be observed experimentally by noting the suppression of the gap voltage in the pumped current-voltage (I-V ) curve as the LO pumping level is increased. Similar observation has already been reported, and attempts were made to estimate the effective temperature of the device using equations of heat transfer between the mixer chip layers. Here, we present an experimental method of quantifying this effect by recovering the effective temperature of the junction through comparing the pumped I-V curves at different pumping levels and fixed bath temperature, with the unpumped I-V curves obtained at varying bath temperatures. We also estimate, for the first time, the effect of heating on the noise temperature as a function of bath temperature and frequency. We show that for typical experimental parameters, the LO heating can increase the double-sideband receiver noise temperature by as much as 20%, and that in the frequency range of the measurements, the effective temperature of the junction at fixed LO power increases linearly with frequency at a rate of 0.5 K/100 GHz.

Noise temperature distribution of superconducting hot electron bolometer mixers**Project supported by the Chinese Academy of Sciences (Grant Nos. GJJSTD20180003 and QYZDJ-SSW-SLH043), the National Key Basic Research and Development Program of China (Grant Nos. 2017YFA0304003 and 2018YFA0404701), the National Natural Science Foundation of China (Grant Nos. 11603081, 11673073, U1831202, and 11873099), and PICS projects between the CAS and the CNRS.

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 (Trec) 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.

Compact and sensitive heterodyne receiver at 2.7 THz exploiting a quasi-optical HEB-QCL coupling scheme

We demonstrate a sensitive and compact terahertz heterodyne detection system based on a quantum cascade laser (QCL) as a local oscillator and a hot electron bolometer (HEB) as a mixer. It relies on an original optical coupling scheme where the terahertz (THz) signal to be detected and the local oscillator (LO) signal are coupled to the HEB from both sides of the integrated lens/antenna mixer. The THz signal of interest impinges on the front side through the silicon lens while the LO onto the rear (air) side. This concept allows us to remove the beam splitter usually employed in terahertz heterodyne receivers. The mixer consists of a Niobium Nitride HEB with a log-spiral planar antenna mounted on the flat side of a hyperhemispherical silicon lens. The local oscillator of the heterodyne detector is a low power consumption and low beam divergence 3rd-order distributed feedback laser with single mode emission at the target frequency of 2.7 THz. The coupling between the QCL and the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity and permits us to pump the HEB into its most sensitive state through the air side of the planar antenna. We have measured a noncorrected double sideband receiver noise temperature of 880 K at 2.7 THz.

10.6 μm heterodyne receiver based on a superconducting hot-electron bolometer mixer and a quantum cascade laser

We report on the development of a heterodyne receiver at mid-infrared wavelength for high-resolution spectroscopy applications. The receiver employs a superconducting NbN hot electron bolometer as a mixer and a room temperature distributed feedback quantum cascade laser operating at 10.6 μm (28.2 THz) as a local oscillator. The stabilization of the heterodyne receiver has been achieved using a feedback loop controlling the output power of the laser. Improved Allan variance times as well as a double sideband receiver noise temperature of 5000 K and a noise bandwidth of 2.8 GHz of the receiver system are demonstrated.

275–500-GHz Wideband Waveguide SIS Mixers

We have successfully demonstrated low-noise and wideband SIS mixers for the 275–500-GHz radio-frequency (RF) band, aiming to cover Atacama Large Millimeter/submillimeter Array band 7 (275–373 GHz) and band 8 (385–500 GHz) simultaneously. The waveguide SIS mixers integrate a multisection impedance transformer with a parallel-connected-twin-junction or single-junction circuits based on Nb/AlN/Nb trilayers with a critical current density of 31 kA/cm2. In order to achieve the targeted broadband performance, we designed an asymmetric one-side waveguide probe placed across a reduced height waveguide with dimensions 100 μm × 580 μm. The shape of the waveguide probe was optimized to have nearly constant impedance at around 35 Ω in the desired RF range. For evaluation of the receiver performance, we have established a dual-band noise temperature measurement system. The system implements a broadband corrugated horn antenna and a 15-dB RF/local oscillator (LO) waveguide coupler based on WR-2.3 (290 μm × 580 μm) waveguide size. The target bandwidth is too wide for typical LO sources at these high frequencies, and, therefore, we applied a dual-band LO injection system utilizing two different LO sources and an LO diplexer. The IF chain uses a cryogenic isolator and a low-noise amplifier with a typical noise temperature of 2.1 K over the 4–8-GHz range. The measured double sideband receiver noise temperature is two to three times the quantum noise at all LO frequencies for both the twin-junction and the single-junction circuits.

An Ultra-High-Sensitivity Superconducting Hot-Electron-Bolometer Heterodyne Receiver at 2.5 THz With an Integrated Low-Power-Consumption Quantum Cascade Laser

We report on the demonstration of an ultra-high-sensitivity superconducting hot-electron-bolometer (HEB) heterodyne receiver at 2.5 THz with a low-power-consumption quantum cascade laser (QCL) as its local oscillator (LO). The 2.5-THz QCL, with an electrical power dissipation of about 0.9 W in continuous wave mode, is integrated with a spiral-antenna-coupled niobium nitride HEB mixer in a single block. The mixer performance is barely affected by heat dissipation from the QCL when the receiver is cryogenically cooled either by a wet LHe Dewar or by a closed-cycle 4-K pulse-tube cooler. Measured with a vacuum setup, the heterodyne receiver exhibits a double sideband receiver noise temperature of 800 K at 2.5 THz with the IR filter contribution corrected, which is approximately 7hυ/kB. And the Allan variance time at 80-MHz noise bandwidth is found to be about 10 s when a proportional-integral-derivative controller is adopted to control the LO power.

Broadband MgB2Hot-Electron Bolometer THz Mixers Operating up to 20 K

We discuss performance of submicron size hot-electron bolometer mixers made from thin MgB2 superconducting films. With a superconducting transition temperature of ∼30 K, such terahertz (THz) mixers can operate with high sensitivity at temperatures up to 20 K. Due to very small dimensions local oscillator power requirements are rather low. In the intermediate frequency band of 1–3 GHz, the double sideband receiver noise temperature is 1600 K at 10 K operation temperature, 2000 K at 15 K, 2500–3000 K at 20 K. The gain bandwidth of such devices is 6 GHz and the noise bandwidth is estimated to be 6–8 GHz.

A 1.4 THz Quasi‐Optical NbN Superconducting HEB Mixer Developed for the DATE5 Telescope

In this paper, the performance of a twin-slot antenna coupled NbN superconducting HEB mixer based on a new device fabrication process is thoroughly investigated. The measured lowest double-sideband receiver noise temperature is about 600 K at 1.3 THz, and reduced to 300 K after eliminating all the quasi-optical losses. The spectral response of the HEB mixer is characterized by a Fourier Transform Spectrometer (FTS) and its calibrated spectrum is in good agreement with the simulated one. In addition, the far-field beam pattern of this HEB mixer is characterized by a near-field measurement technique. The measured results agree well with the simulations too.

Performance of the Caltech Submillimeter Observatory Dual-Color 180–720 GHz Balanced SIS Receivers

In this paper, we report on balanced SIS receivers covering the astronomical important 180-720 GHz submillimeter atmospheric window. To facilitate remote observations and automated spectral line surveys, fully synthesized local oscillators are employed. High-current-density Nb-AlN-Nb superconducting-insulating-superconducting (SIS) tunnel junctions are used as the mixing element. The measured double-sideband (DSB) 230 GHz receiver noise temperature, uncorrected for optics loss, ranges from 50 K at 185 GHz, 33 K at 246 GHz, to 51 K at 280 GHz. In this frequency range the mixer has a DSB conversion gain of 0 ±1.5 dB. The measured 460 GHz double-sideband receiver noise temperature, uncorrected for optics loss, is 32 K at 400 GHz, 34 K at 460 GHz, and 61 K at 520 GHz. Similar to the 230 GHz balanced mixer, the DSB mixer conversion gain is 1 ±1 dB. To help optimize performance, the mixer IF circuits and bias injection are entirely planar by design. Dual-frequency observation, by means of separating the incoming circular polarized electric field into two orthogonal components, is another important mode of operation offered by the new facility instrumentation. Instrumental stability is excellent supporting the LO noise cancellation properties of the balanced mixer configuration. In the spring of 2012 the dual-frequency 230/460 SIS receiver was successfully installed at Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, USA.

Development and testing of Band 10 receivers for the ALMA project

The production model of a dual polarization heterodyne receiver for the Atacama Large Millimeter/submillimteter Array (ALMA) telescope has been developed to operate in the 787–950GHz frequency band. The receiver uses two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. A terahertz time domain spectrometer was used to characterize our NbTiN film for the tuning circuit design, which revealed that the complex conductivity of the film is described by the Mattis-Bardeen theory including a finite scattering time of 15fs and a superconducting gap with a gap ratio 2Δ/kBTC∼4.0. Tens of these receivers (out of the total production number of 73) have been successfully produced, and their performance is well within the stringent ALMA requirements. The best achieved DSB receiver noise temperature is 125K, corresponding to about 3hf/kB for 4K operation. One of Band 10 receivers has successfully been installed in the ALMA antenna for a test observation.

Hot electron bolometer heterodyne receiver with a 4.7-THz quantum cascade laser as a local oscillator

We report on a heterodyne receiver designed to observe the astrophysically important neutral atomic oxygen [OI] line at 4.7448 THz. The local oscillator is a third-order distributed feedback quantum cascade laser operating in continuous wave mode at 4.741 THz. A quasi-optical, superconducting NbN hot electron bolometer is used as the mixer. We recorded a double sideband receiver noise temperature (TrecDSB) of 815 K, which is ∼7 times the quantum noise limit (hν2kB) and an Allan variance time of 15 s at an effective noise fluctuation bandwidth of 18 MHz. Heterodyne performance was confirmed by measuring a methanol line spectrum.

Noise temperature and beam pattern of an NbN hot electron bolometer mixer at 5.25 THz

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.

A Low-Noise Terahertz SIS Mixer Incorporating a Waveguide Directional Coupler for LO Injection

We have developed a low-noise heterodyne waveguide Superconductor-Insulator-Superconductor (SIS) mixer with a novel local oscillator (LO) injection scheme for the Atacama Large Millimeter/submillimeter Array (ALMA) band 10, over the frequency range 0.78–0.95 THz. The SIS mixer uses radio frequency (RF) and LO receiving horns separately and a waveguide 10 dB LO coupler integrated in the mixer block. The insertion loss of the waveguide and coupling factor of the coupler were evaluated at terahertz frequencies at both room and cryogenic temperatures. The double-sideband (DSB) receiver noise temperatures were below 330 K (7.5hf/kB) at LO frequencies in the range 0.801–0.945 THz. The minimum temperature was 221 K at 0.873 THz over the intermediate frequency range of 4–12 GHz at an operating temperature of 4 K. This waveguide heterodyne SIS mixer exhibits great potential for practical applications, such as high-frequency receivers of the ALMA.

Integrated 585-GHz Hot-Electron Mixer Focal-Plane Arrays Based on Annular Slot Antennas for Imaging Applications

We have developed 585-GHz quasi-optical mixers and focal-plane arrays (FPAs) comprised of planar annular slot antennas (ASAs) with integrated niobium hot-electron bolometers for imaging applications. In order to optimize the single-element mixer design, the embedding impedance of the single ASA presented to the bolometer is analyzed using the induced electromotive force (EMF) method by including the antenna feed contribution. This approach has been further expanded to analyze the ASA self-impedance and mutual impedance in an array by utilizing the even-odd mode analysis. In addition, the far-field radiation patterns of the ASAs mounted to an extended hemispherical high-resistivity silicon lens have been calculated using the ray-tracing techniques. The details of circuit design and fabrication are presented in this study. Single mixer element measurement results have shown that a conversion gain of -11.9 dB and a double-sideband (DSB) receiver noise temperature of ~650 K have been achieved. Initial array imaging experiment results are presented and show excellent agreement with theory and simulation data. A spatial resolution of ~2.75 mm has been demonstrated at 585 GHz for a 1-D mixer FPA that is capable of diffraction-limited imaging. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -factor measurements show DSB mixer noise temperatures of 1675 and 3517 K with mixer conversion gains of -14.73 and -17.74 dB, respectively, have been obtained for two adjacent elements in a mixer array, which is comparable to the results reported in the literature.

Low Noise Receivers Based on Superconducting Niobium Nitride Hot Electron Bolometer Mixers from 0.65 to 3.1 Terahertz

SUMMARY Low noise terahertz (THz) receivers based on superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixers have been designed, fabricated and measured for applications in astronomy and cosmology. The NbN HEB mixer consists of a planar antenna and an NbN bridge connecting across the antenna’s inner terminals on a high-resistivity Si substrate. To eliminate the influence of direct detection and instability of the local oscillation (LO) power, a wire grid has been used to change the input LO power for compensating the shift of bias current during Y-factor measurement. The double sideband (DSB) receiver noise temperatures at 4.2 K without corrections have been measured from 0.65 to 3.1 THz. The excess quantum noise factor β of about 4 has been obtained, which agrees well with the calculated value. Allan variance of the HEB has been characterized, and Allan time TA longer than 0.4 s is obtained. We also estimated the temperature resolution of the HEB from the Allan variance and obtained the minimum temperature resolution of 1.1 K using a Gunn oscillator with its multipliers at 0.65 THz as an LO source.

Low Noise Receivers at 1.6 THz and 2.5 THz Based on Niobium Nitride Hot Electron Bolometer Mixers

Low noise receivers based on superconducting niobium nitride (NbN) hot electron bolometer (HEB) mixers have been designed, fabricated and measured in the terahertz (THz) frequency range for applications in astronomy and cosmology. The NbN HEB mixer consists of a planar antenna and an NbN bridge connecting across the antenna's inner terminals on high-resistivity Si substrates. Double sideband (DSB) receiver noise temperatures of 920 K at 1.6 THz and 1630 K at 2.5 THz have been obtained at 4.2 K without corrections. Effects of Parylene C AR coating on the lens have been studied; with such a coating a lowest DSB receiver noise temperature of 1135 K at 2.5 THz has been obtained at 4.2 K.

3.4 THz heterodyne receiver using a hot electron bolometer and a distributed feedback quantum cascade laser

We report a heterodyne receiver using a superconducting NbN hot electron bolometer (HEB) integrated with a tight winding spiral antenna as mixer and a distributed feedback (DFB) terahertz quantum cascade laser (QCL) operating at 3.42 THz as local oscillator. The aim is to demonstrate the readiness of both devices for the detection of OH lines at 3.5 THz in a real instrument. We show that the improved single-spot beam of the terahertz QCL can easily pump the HEB mixer. We measured a double sideband receiver noise temperature of 2100 K at the optimum local oscillator power of 290 nW. This noise temperature can be further reduced to 1100 K if we correct the loss due to the use of an uncoated lens, and the losses of the window and the air. Therefore, the combination of a HEB and such a DFB QCL can in principle be used to detect an OH line at 3.5 THz. However, a high input power of several watts, which is needed to operate the QCL in a liquid-helium cryostat, poses a big challenge to the receiver stability.

Low noise NbN hot electron bolometer mixer at 4.3THz

We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300K at the optimum local oscillator (LO) power of 330nW, which is about 12 times the quantum noise (hν∕2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.