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Applied Physics Letters

Broadband generation of tunable Josephson radiation at microwave frequencies

C. Varmazis, James E. Lukens, Thomas F. Finnegan

Published Jun 15, 1977• 5 citations
Publisher

Abstract

Radiation with an integrated power of about 10−12 W has been obtained from a microbridge Josephson junction. The output can be continuously tuned between 2 and 12 GHz. The frequency and current dependence of radiated power and linewidth are in disagreement with the resistively shunted junction model.
DOI
10.1063/1.89276

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Josephson radiation emitted from superconducting microbridges and coupled two-bridge junctions has been investigated at microwave frequencies. The radiation linewidth Ɗf and total radiation power P are found to vary with the output coupling controlled by a tuning stub in the cavity, indicating feedback-induced effects due to the radiation fields. We have found (Ɗf)min ~ 900 kHz, Pmax ~ 0.9 x 10-12 W for the single microbridge and (Ɗf)min ~ 60 kHz, Pmax ~ 5 x 10-12 W for the coupled bridges. The enhancement of radiated power and line-narrowing in the coupled bridges are attributed to coherent behaviour of the junctions.
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Measurements at 3 GHz of the microwave properties of a superconducting thin-film microbridge coupled to a narrowly tuned strip-line resonator (coupled Q approximately 10 3 ) indicate that such a device displays the same variations in small-signal impedance as predicted by the resistively shunted junction model of a Josephson weak-link. Whenever this impedance becomes negative the microbridge is found to generate microwave radiation whose frequency is determined not by the junction bias voltage but by the natural resonance of the strip-line.