Search

We are developing a new superconducting amplifier technology for radio astronomy instruments called the Traveling-Wave Kinetic Inductance Parametric (TKIP) amplifier. Invented at Caltech/JPL, recent laboratory demonstrations have resulted in near quantum-limited noise performance over more than an octave of microwave bandwidth and operating temperatures as high as 3 Kelvin. These amplifiers have the potential to be used as front-end replacements for ALMA's mm/sub-mm SIS receivers and intermediate frequency (IF) amplifiers, and for multiplexing faint signals from focal-plane arrays of single-photon detectors on space telescopes such as NASA's Origins Space Telescope (OST). The enhanced observational capabilities that would be enabled by TKIP front-end amplifiers on ALMA would tremendously benefit ALMA science across all bands.

The field of submillimeter-wavelength astronomy is blossoming thanks to major investments such as the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Herschel Space Telescope. These projects were enabled by the development of very sensitive receivers, especially those using Superconductor-Insulator-Superconductor (SIS) tunnel junction diodes. Here I review some of the challenges that were faced in pushing this technology from its first demonstrations around 100 GHz to its upper frequency limit beyond 1.2 THz.

We have made close-packed far-infrared MKID arrays with ~ 250 pixels using TiN on silicon. Measurements show a large scatter in quality factor arising from crosstalk. This is confirmed by pump-probe experiments and EM simulations. Our new shielded resonator designs show very low crosstalk levels.

Superconducting microresonators are drawing increasing attention for use in sensitive THz detection, especially for astronomical applications. These are relatively simple thin-film lithographically produced devices that are amenable to large-scale microwave frequency multiplexing. Indeed, such resonators have very high quality factors, in the range 10^4 to 10^6, potentially allowing 10^3 to 10^4 resonators to be multiplexed using a single cryogenic low-noise amplifier (HEMT). The resonators may themselves serve as detectors given appropriate coupling of the signal energy, or the resonators may be used to multiplex a broad range of other devices such as SIN or SIS tunnel junction detectors, SQUID preamplifiers for TES bolometers, etc. One of the major advantages of microwave frequency multiplexing is that much of the complexity of the readout system is transferred to room temperature, where it is now feasible to produce readouts with very high channel counts using FPGA digital signal processing along with fast, high-resolution ADCs and DACs. This presentation will give an overview of the topics described above, including an introduction to the basic physics of superconducting microresonators and their noise mechanisms, and as a concrete example will describe the development of a 2.5 kilopixel millimeter-wave multicolor camera system for the Caltech Submillimeter Observatory.

In this paper, we describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor-insulator-superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180° hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180° IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent giving uncorrected receiver noise temperature of better than 115 K (double sideband) at 528 GHz for both the polarizations.

We report on the design and performance of a 530-GHz balanced SIS mixer, the first balanced mixer in this frequency range. This quasi-optical balanced mixer utilizes a cross-slot antenna on a hyperhemispherical substrate lens with eight superconductor-insulator-superconductor (SIS) junctions and a 180° lumped element IF hybrid circuit. The local oscillator (LO) and the radio frequency (RF) signal, orthogonal in polarization to each other, are coupled to the mixer using a wire-grid polarizer. The noise performance of the mixer is excellent, giving an uncorrected receiver noise temperature of 105 K (DSB) at 528 GHz.

We describe a new dual-polarized slot antenna to be used with quad-optical devices such as superconductor-insulator-superconductor (SIS) mixers at millimeter and submillimeter wavelengths. The radiation and impedance characteristics of the antenna were obtained from a moment-method calculation. The antenna has an excellent radiation pattern, a low impedance, wide bandwidth, and low cross polarization.

We describe the design, simulation, fabrication, and performance of a 96-GHz ortho-mode transducer (OMT) to be used for the Polatron-a bolometric receiver with polarization capability. The OMT has low loss, good isolation, and moderately broad bandwidth, and its performance closely resembles simulation results.

Photon-induced current correlations in SIS detectors can result in an output noise that is greater or less than shot noise. Evidence of these correlations had been observed for 100 GHz rf by accurate noise measurements as reported in our previous work. We now present a detailed analysis of these current correlations for frequencies between 100 and 500 GHz. We also report new measurements of photon-induced noise in a 490 GHz SIS mixer, and discuss the Gaussian beam techniques used to eliminate the thermal background radiation. For small 490 GHz rf power, the output noise is equal to shot noise. The results of the 100 and 490 GHz photon noise measurement are summarized in context to shot noise and the effect of the current correlations predicted by the theoretical model.