Superconducting on-chip spectrometers have both imaging and spectroscopic capabilities. In general, the broadband signal coupled from an antenna goes through frequency dispersion via a series of filters that are connected with superconducting detectors like kinetic inductance detectors or bolometers. The filters have the same relative bandwidth, which determines the frequency resolution of the spectrometer. We here present the design and simulations on the twin-slot antenna, CPW-to-microstrip transition, and a ten-channel filter-bank of a verification-stage terahertz spectrometer chip at 350 GHz. The simulation results of the antenna and transition showed low return loss, and the simulation results of the ten-channel filter-bank show that each channel has good readout independence and coupling strength. These designs and simulations can provide assistance for the future development of terahertz on-chip spectrometer.
As one of the backend modules aboard the China Space Station Telescope, the high-sensitivity terahertz detection module (HSTDM) needs to be rationally scheduled to conduct various observation tasks to fulfill and maximize its scientific goals. This is because HSTDM cannot operate simultaneously with other modules, and the observable time windows determined by constrained and changeable conditions are randomly distributed and limited; even worse, the total allocated time is estimated to account for less than 10% of the total in-orbit time. We develop a modified genetic algorithm (MGA) to better solve this problem. Compared with conventional genetics algorithm (CGA), the core uniqueness of this method are as follows: (1) reduce the search space of chromosomes by pre-calculating the observable time windows of observing objects; (2) accelerate the exploration and exploitation of chromosomes by a transformation process that reduces the chromosome length through recombination of non-zero valued genes, followed by increasing the initial population diversity through the proposed similarity avoidance based population generation method and then by adopting stochastic universal sampling and elitism selection combined parents selection method; and (3) design a compound fitness function that can simultaneously achieve three optimization criteria through evolution process. The effectiveness of the proposed method is validated on a simulated scenario, and performance comparisons with CGA suggest that MGA can generate more profitable solutions (as much as 46% improvement) in fewer (as much as 90% reduction) generations.
The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs ([U]BV, RIZ, YJH) providing a spectral resolution of ∼100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 μm with the goal of extending it to 0.35-2.4 μm with the addition of an U arm to the BV spectrograph and a separate K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Modularity and fibre-feeding allows ANDES to be placed partly on the ELT Nasmyth platform and partly in the Coudé room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature’s fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of almost 300 scientists and engineers which include the majority of the scientific and technical expertise in the field that can be found in ESO member states.
Superconducting transition-edge sensors (TESs) are highly sensitive detectors and can detect electromagnetic wave radiations from millimeter/submillimeter, optical to 𝑥/γrays, suitable for cosmology, astrophysics, quantum information, and biosensing. In principle, thousands of TESs even more are required to enhance the detection efficiency for large-scale survey. Among other multiplexing schemes, microwave SQUID multiplexer (μMUX), consisting of resonators and RF SQUIDs, has a bandwidth of several GHz, thus multiplexing factor on the order of thousands, more suitable for readout of large TES arrays. We designed and fabricated superconducting coplanar waveguide (CPW) resonators with a high qualityfactor and second-order gradient RF SQUID with two inductive coupling structures respectively. Then, we optimized the critical current density of the Josephson junction and measured the mutual inductance parameters of the second-order gradient structure SQUID, which are consistent with the simulation results. Finally, we fabricated a cryogenic μMUX chip based on RF SQUID and resonator. We discussed the results of the development of μMUX in more detail.
Microwave kinetic inductance detectors (MKIDs) can detect photons ranging from terahertz, infrared, optical to X-ray frequencies. And it has the advantages of high sensitivity, easy frequency-domain multiplexing (FDM) readout, and simple structure for large-format arrays. With these advantages MKIDs are becoming the choice of incoherent detectors in astronomy such as imaging cameras and broadband imaging spectrometers. In this paper, we introduce the design and fabrication of a 5-THz 10×10 MKIDs array on a single chip from an 80-nm-thick aluminum (Al) superconducting film based on a high resistance silicon substrate. Each pixel is a quarter-wavelength resonator with its short-circuited end integrated with a 5-THz dipole antenna. The noise performance of the MKIDs is measured at 200-mK using both phase readout and amplitude readout, giving an electrical NEP ~10−17 W/Hz0.5. Detailed results will be presented.
Lens integrated twin slot antennas have been widely used in superconducting transition edge sensor (TES) detectors due to its high directivity and low cross-polarization. In this paper, we present the design and simulation of a 210 GHz dual-polarized twin slot antenna for TES detectors. We used Ansoft HFSS to simulate the return loss and isolation of the dual-polarized twin slot antenna. The results show that the return loss of the dual-polarized twin slot antenna is less than -15 dB and the isolation is great than 10 dB in the frequency range from 170 GHz to 230 GHz. We also used FEKO to simulate the beam pattern of the dual-polarized twin slot antenna integrated with a silicon lens with a diameter of 5 mm. After optimizing the extended length of the silicon lens, a near Gaussian beam with a half power beam width (HPBW) of 19.4 degrees and a side lobe level of 17.3 dB was obtained. In addition, we designed and simulated an air bridge that is used to transmit the signals received by the twin slot antennas in the orthogonal directions. We find that the transmission coefficient of the air bridge is close to 0 dB and the isolation in the orthogonal directions exceeds 35 dB.
Superconductor–insulator–superconductor (SIS) mixers remain the choice of heterodyne mixers for single-dish telescopes and interferometers at millimeter and submillimeter wavelengths. Compared with conventional Nb/AlOx/Nb superconducting tunnel junctions, Nb/AlN/NbN ones have larger gap voltage and may reach critical-current density beyond 10kA/cm2, which are both of particularly interest in developing broadband SIS mixers. Here we report on the design and measurement of an SIS mixer based on Nb/AlN/NbN parallel connected twin junctions (PCTJ) incorporating NbTiN/SiO2/Al microstrip circuit. The junctions have a gap voltage of 3.18mV and a critical-current density of 15kA/cm2. The measured receiver noise temperature reach 5hν/kB among 200-260GHz band, and the mixer’s fractional bandwidth is about 40% centered at 230GHz.
Microwave Kinetic Inductance Detectors (MKIDs), just like a planar resonance cavity resonating at a microwave frequency, are emerging as a kind of high-sensitivity detector suitable for large format arrays at terahertz (THz) wavelengths. There are two types of MKIDs, namely distributed (or antenna-coupled) MKIDs and lumped-element MKIDs (aka LeKIDs). Various superconducting thin films (such as Al, TiN, NbTiN, NbN, and Nb) have been investigated for MKIDs. They do work so long as the detected photon energy exceeds their energy gap, but their response and noise behaviors are yet to be fully understood. Here we report on the design, fabrication, and characterization of distributed and lumped-element MKIDs made of NbTiN superconducting film. Detailed simulation and measurement results will be presented.
Microwave kinetic inductance detectors (MKIDs) are promising low-temperature superconducting detectors because of high sensitivity, easy frequency-domain multiplexing (FDM) readout, and simple structure for large-format arrays. Each pixel of the MKID array is a microwave resonator, and the FDM technology makes the resonant frequencies of all resonators read out by one feedline. However, there are often crossovers, missing, and overlapping phenomena between resonance curves. As a prerequisite for imaging, it is necessary to confirm the correspondence between the resonance frequency point and the physical position of the pixel. In this paper, by designing and using an 8×8 LED dot matrix, a fast pixel recognition of an 8×8 MKID array is realized. In addition, the I-V characteristics of the AlGaInP red Light-emitting diode (LED) used in the experiment at different low temperatures are characterized. Finally, through the MKID that has achieved pixel positioning, and the image of LED multi-point lighting is obtained.
We design and fabricate a 350GHz 8×8 Al Microwave Kinetic Inductance Detector (MKIDs) array for the demonstration of its characteristics, mainly focus on the quasiparticle lifetime of the resonators. The quasiparticle lifetime data is collected by measuring a resonator’s phase response to a LED pulse at resonant frequency in a dilution refrigerator cooled to mK stage. We also measure and discuss the influence of various parameters on the change of quasiparticle lifetime, including different LED voltage supply, bath temperature of the MKIDs, and superconducting film thickness.
Microwave Kinetic Inductance Detectors (MKIDs), with high sensitivity and relatively simple frequency multiplexing, are emerging as a kind of large-array detectors in the terahertz (THz) band. An MKID, like a superconducting resonator, is composed of a planar capacitor and inductor that are made from superconducting films. The energy gap of the superconducting film for the planar inductor (at least part of it) is lower than the energy of photons to be detected. The kinetic inductance of the superconducting film irradiated by the photons is increased, shifting the resonance frequency toward a lower frequency. The frequency shift is proportional to the kinetic inductance fraction, i.e., the ratio of the kinetic inductance to the total inductance of the planar superconducting inductor. In this paper, we thoroughly investigate the kinetic inductance fraction for lumped-element and antenna-coupled MKIDs, which are both made from NbTiN. The detailed simulation, calculation, and measurement results will be presented.
Superconductor-insulator-superconductor (SIS) mixers, with nearly quantum-limited sensitivity, have been playing an important role in Terahertz astronomy. For practical THz SIS receivers, however, the measured noise temperatures are sometimes higher than the expected value. The extra noise is mainly due to considerable RF noise contribution from the receiver components such as beam splitter, Dewar window, and infrared filter. In this paper, we mainly present the simulation and measurement results of the three components with different materials and thicknesses. Their noise contributions are also analyzed.
Besides the sensitivity nearly approaching the quantum limit, the intermediate-frequency (IF) bandwidth is of particular interesting for Superconductor-insulator-superconductor (SIS) mixers for radio astronomy research. In this paper, we are going to present the characteristic of IF bandwidth of two type of NbN SIS mixers, Long distributed junctions and Parallel-connected twin junctions. Firstly, the relative mixer gain are measured with different IF load impedance (25Ω, 50Ω, 75Ω) for both two SIS mixers. And also the mixers gain with different IF load impedance is simulated to get the optimum IF load impedance over a relative large IF bandwidth (2-15GHz). Finally, an IF matching circuit is designed and measured associating with SIS mixers, the measurement results show that the mixers gain are flatter over a large IF bandwidth than with 50Ω IF load impedance.
Microwave Kinetic Inductance Detectors (MKID) are a promising low temperature superconducting detector because of high sensitivity, easy frequency-domain multiplexing and simple structure for large-format arrays. To develop large-format THz detectors for China’s Antarctic THz telescope, we have preliminarily designed an aluminum 64-pixel MKID array operating at the 350 GHz band. In this paper, the characteristics of the MKID array are thoroughly measured.
In this paper, we will introduce a dual-THz-band SIS (Superconductor-Insulator-Superconductor) heterodyne radiometer system developed for the atmospheric profiling synthetic observation system project (APSOS). This THz system is intended to have a durable and compact design to meet the challenging requirements of remote operation. The system as well as its major components such as antenna tipping, quasi-optics, cryogenics, SIS mixers and FFTS backend will be discussed thoroughly. Some scientific simulation focusing on the atmospheric profiling components at THz bands will also be investigated.
KEYWORDS: Signal processing, Sensors, Field programmable gate arrays, Signal detection, Signal to noise ratio, Terahertz radiation, Interference (communication), Superconductors, Amplifiers, Signal generators
Terahertz Superconducting Imaging Array (TeSIA) is a project for the development of a large THz direct-detection array for mapping observations. The prototype of TeSIA is an 8×8 pixel direct-detection array operating at the 850 μm band, incorporating THz superconducting detectors such as kinetic inductance detectors (KIDs) and transition edge sensors (TES). KIDs have the advantage that only a broadband low noise cryogenic amplifier is needed at low temperature for the readout system, and hundreds of pixels could be readout simultaneously by the frequency-division multiplexing (FDM) technique. The readout system for a KIDs array is composed of several parts like excitation signal generating, intermediate frequency (IF) circuit, baseband signal acquisition and processing. Excitation signal is a kind of comb signal carrying various frequencies corresponding simply to resonant frequencies of the detectors. It is generated in baseband with a bandwidth covering all KIDs and up-converted to microwave frequency (about several gigahertz) to feed the detectors. With THz radiation, the forward transmission coefficient (S21) of all KIDs varies and the variation can be measured through the comb signal. Fast Fourier transform (FFT) with pipeline structure will be used to process the baseband excitation signal in real time. Consequently, the radiation intensity can be estimated by monitoring the signal amplitude and phase of the corresponding frequency channels. In this paper we will present mainly the design ofan electronic readout system for the 8×8 pixel array.
As a new attempt to expand wireless transmission channel bandwidth, a submillimeter-wave communication experiment
has been carried out by using techniques of frequency multiplication of millimeter-wave signal source and high-sensitivity
superconducting SIS (Superconductor-Insulator-Superconductor) receiver. The transmitter consists of a 500-GHz frequency quintupler and a 93-GHz varactor-tunable Gunn oscillator with its output frequency modulated via a 10-14 MHz signal source, while the 500-GHz SIS receiver has an IF (Intermediate Frequency) band of 1.1-1.7 GHz and an
overall system noise temperature below 400 K. A theoretical analysis is given to prove the principle and engineering
feasibility of the experimental communication system. The measured spectra of the received FM (Frequency
Modulation) signals with modulation frequencies of 10-14 MHz on a downconverted IF carrier of 1.6 GHz show that
effective direct frequency modulation on a transmitting submillimeter-wave carrier of 466 GHz and the reception of the
submillimeter-wave FM signals by the 500-GHz SIS receiver have been successfully realized.
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region.
Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.
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