EXPONENTIALLY TAPERED JOSEPHSON FLUX-FLOW OSCILLATOR

We introduce an exponentially tapered Josephson flux-flow oscillator t hat is tuned by applying a bias current to the larger end of the junct ion. Numerical and analytical studies show that above a threshold leve l of bias current the static solution becomes unstable and gives rise to a train of fluxons moving toward the unbiased smaller end, as in th e standard flux-flow oscillator. An exponentially shaped junction prov ides several advantages over a rectangular junction including: (i) sma ller linewidth, (ii) increased output power, (iii) no trapped flux bec ause of the type of current injection, and (iv) better impedance match ing to a load.