H. van de Stadt

Heterodyne mixing with Nb tunnel junctions above the gap frequency

The noise and gain of a heterodyne waveguide mixer employing Nb/Al2O3/Nb superconducting tunnel junctions with an on‐chip integrated tuning element are measured and analyzed at 680–750 GHz and at 840 GHz. The lowest receiver noise temperatures are 400 K (double side band) at 720 GHz and 1500 K (3000 K including the beam splitter loss) at 840 GHz. We compare data of the pumped I–V curves with the quantum theory of mixing and demonstrate good agreement at frequencies well above the gap frequency.

Integrated sub-MM wave receivers

The concept of a fully integrated superconducting receiver looks very attractive for sub-mm space astronomy where low weight, power consumption and volume are required. The possibility to integrate on a few chips the different planar components: a SIS mixer, a superconducting local oscillator (LO), an intermediate frequency amplifier followed by superconducting circuits for digitizing and processing of down converted signals, is discussed. A first implementation of a real integrated quasioptical receiver for frequencies up to 500 GHz is described. The one-chip receiver comprises a double dipole antenna, parallel biased SIS array mixer and Josephson Flux Flow Oscillator (FFO) with matching circuits. The results of extensive investigations of the integrated receiver as well as design and investigation of novel superconducting elements are presented.<<ETX>>

An integrated 500 GHz receiver with superconducting local oscillator

An integrated quasioptical receiver consisting of a planar double-dipole antenna, SIS mixer and superconducting Flux-Flow Oscillator (FFO) with matching circuits has been designed, fabricated and tested in the frequency range 420-530 GHz. The integrated receiver is very suitable for space applications because of its low size, mass and power consumption. All components of the receiver are integrated on a 4 mm/spl times/4 mm/spl times/0.2 mm crystalline quartz substrate using a single Nb-AlO/sub x/-Nb trilayer. The successful operation of the integrated receiver comprising a number of new crucial elements has been demonstrated. A DSB noise temperature as low as 140 K at 500 GHz and a tuning range of more than 100 GHz have been obtained. A comparison of the FFO with conventional external LO has been performed.

Analysis of Nb superconductor-insulator-superconductor tunnel junctions with Al striplines for THz radiation detection

We study the gain and noise of a receiver consisting of a niobium junction embedded in an aluminum impedance matching circuit. The junction is operated in a waveguide mount with an adjustable backshort. The uncorrected double side band noise temperatures are 940 K to 1388 K for 820 to 980 GHz respectively. The total optical loss is obtained from the losses of the individual components, the losses in the stripline are calculated using the Reuter-Sondheimer equation in the extreme anomalous limit. The embedding impedance follows from the pumped curves and the Tucker equations which are also used to determine the noise and gain of the junction. The main limitation to the receiver sensitivity is shown to be the loss in the aluminum circuit.

Direct current heating in superconductor-insulator-superconductor tunnel devices for THz mixing applications

DC heating effects in superconductor–insulator–superconductor (SIS) tunnel junctions are studied by comparing junctions sandwiched between niobium or aluminum layers. With niobium a temperature rise of several Kelvin is observed, which is reduced by an order of magnitude by using aluminum. A simple model satisfactorily explains this observation and predicts a 30% increase in the subgap current due to the elevated temperature. At the operating voltage for heterodyne mixing the receiver noise temperature increases by only 2%.

A low noise 410-495 GHz Nb/Al/sub 2/O/sub 3//Nb SIS waveguide mixer

The noise and gain of a heterodyne waveguide mixer using Nb/Al/sub 2/O/sub 3//Nb superconducting tunnel junctions were measured in the 400-500-GHz frequency range. Three different arrays of two junctions in series are analyzed. The minimum receiver noise temperature is 120 K DSB at 480 GHz, measured with an array having integrated tuning stubs. The authors compare data of the pumped I-V curves with the Werthammer-Tucker theory and demonstrate an excellent agreement at frequencies up to 500 GHz. For an array without integrated tuning stubs. a mixer noise temperature of 90+or-30 K and a DSB mixer gain of -12.5+or-0.6 dB were measured. A comparison of the measured gain versus bias voltage with the quantum theory of mixing shows good qualitative agreement, indicating the applicability of this theory to Nb tunnel junctions up to 500 GHz. The noise temperature of an array with a lower gap voltage is 220 K at 495 GHz. This frequency is 85% of the reduced gap frequency, indicating that Nb superconductor insulator-superconductor (SIS) mixers can be used up at least the gap frequency of 680 GHz.<<ETX>>

Heterodyne detection at 337 μm in epitaxial GaAs

Abstract The observation and quantative measurement of optical heterodyne detection at 337 μm using a HCN laser and an epitaxial n-type GaAs photoconductor are reported. The measured NEP amounted 1.4 × 10−14 W Hz−1.

A Common-User Submillimeter Receiver For UKIRT

A submillimeter receiver, to be used as common-user receiver for UKIRT and the UK-NL mm telescope at Mau-na Kea, Hawaii, is here described. The receiver operates at two submm frequency bands using one backward wave oscillator (carcinotron) and a doubler. It utilizes a bath cryostat coupled to a closed cycle cooler for cooling of the mixers and preamplifiers. All main receiver components are microprocessor controlled in order to provide reliable and efficient operation at the high altitude observatory.

A single-sideband optical balanced mixed

An optical single-sideband mixer, operating at 6328 A and utilizing two balanced heterodyne mixers, has been constructed. The sideband suppression ratio was measured to be typically about 25 dB and an optimal ratio of 54 dB was achieved.

Low noise Nb-SIS mixers at far above the gap frequency

There are great interests in developing Nb SIS mixers because of the extremely low noise temperatures and because of the need of low local oscillator (LO) power. Several groups have demonstrated experimentally that Nb SIS mixers with integrated tuning elements can perform near the quantum noise limit up to the Nb gap frequency (/spl sim/700 GHz). Beyond this frequency, a major loss will take place in the tuning elements, which are Nb-SiO/sub 2/-Nb micro-striplines, because the incoming photons can break the Cooper-pairs, thus increasing the surface resistance of the Nb strips. Applying highly conductive Al instead of Nb for a stripline can reduce the loss since the former has a lower surface resistance at higher frequencies. In this work, we report the fabrication of waveguide Nb SIS mixers with Al striplines and heterodyne measurement results around 1 THz.