Design and fabrication of Cherenkov flux-flow oscillator.

The Josephson Flux-Flow Oscillator (FFO) has been used as an on chip local oscillator at frequencies up to 650 GHz. The FFO linewidth of about 1 MHz w as measured in the resonant regime at V < 915 mu V for niobium - aluminum o xide - niobium tunnel junctions, while considerably larger values were repo rted at higher voltages. To overcome this fundamental linewidth broadening we propose a novel on chip Cherenkov radiation flux-flow oscillator (CRFFO) . It consists of a long Josephson junction and a superconducting slow wave transmission line that modifies essentially the junction dispersion relatio n. Two SIS detectors are connected both to the long Josephson junction and the transmission line to evaluate available microwave power. The output pow er coming both from the long junction and the transmission line is estimate d at different bias conditions.