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Japanese Journal of Applied Physics

Phase Locking of SWL Array Junctions in Submillimeter Mixing

Shinji Kodaira, Junji Inatani, Kiyomi Sakai, Toshiaki Fukushima

Published Mar 1, 1990• 1 citation
Publisher

Abstract

We have fabricated a submillimeter mixer with two SWL (short-weak-link) junctions connected in series. This mixer has been used for a 337 GHz fundamental mixing. It has been found that these two junctions independently contribute the IF (intermediate frequency) output when the applied LO (local oscillator) power is small, but that they behave just as a single junction for the increased LO power.

DOI
10.1143/jjap.29.l463

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We have fabricated a submillimeter mixer with two SWL (short-weak-link) junctions connected in series. This mixer has been used for a 337 GHz fundamental mixing. It has been found that these two junctions independently contribute the IF (intermediate frequency) output when the applied LO (local oscillator) power is small, but that they behave just as a single junction for the increased LO power.
A new type of harmonic mixer using a series array of short superconducting weak-links is proposed for mixer applications at far-infrared and submillimeter-wave frequencies. The problem of limited mixer dynamic range can be eliminated by the use of a Josephson junction series array structure. Using a eleven-element series array, a preliminary experiment on harmonic mixing was carried out for two signals at 105.9 GHz and 5.4-12.6 GHz. IF (intermediate frequency) output was measured for each harmonic order from 9th to 19th by optimizing local power and bias voltage. In this experiment, 5-dB heightening of the signal-to-noise ratio was obtained at the IF output when the harmonic mixing order n was equal to the series element number, N=11.>
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A theoretical analysis of harmonic mixing in a quasiparticle tunnel junction at Vbias=0 shows that harmonic mixing for submillimeter frequencies is a viable alternative to fundamental mixing. It is also shown that the signal gain from the first harmonic above the pump frequency to the intermediate frequency is independent of the embedding admittance at the pump frequency. In fact, we show that the five-port model reduces to the three-port model as a result of the inversion symmetry of the I-V curve and, moreover, no large-signal analysis is necessary. Full simulations of harmonic mixing using a five-port model confirm these results. The simulations have been done for the case of a superconductor-insulator-normal junction in which there is no pair current interference. For this type of harmonic mixer we show that the local oscillator (LO) power requirement can be less than a fundamental mixer operating at the same signal frequency, which is particularly useful in circumventing the problems of high-frequency LO power generation.
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