Detection of mm and submm wave radiation from soliton and flux-flow modes in a long Josephson junction

The authors report on the coupling of millimeter and submillimeter waves from a long (3- mu m*350- mu m) Josephson junction to a small (2- mu m*2- mu m) superconductor-insulator-superconductor (SIS) junction by using a center-fed interdigital capacitor. Coupled power at around 100 GHz and 261 GHz was observed. Experiments confirm that the critical current density j/sub c/ of a long junction determines the fluxon motion. Coupled irradiation (>3nW) at around 100 GHz, which corresponds to resonant soliton oscillations in low j/sub c/ samples (250 A/cm/sup 2/ to 1000 A/cm/sup 2/), is detected by the SIS junction. The incident power to the SIS detector junction could be tuned with only little frequency pulling by adjusting the current bias of the oscillator. For j/sub c/>1000 A/cm/sup 2/, coupled radiation at around 100 GHz (about 3 nW) and 261 GHz (4.6 nW), from flux-flow oscillations, is also clearly seen. Flux-flow radiation at 350 GHz is also observed. It is concluded that a large j/sub c/ value is preferable for high-frequency flux-flow oscillators. >