Spectral characteristics of noisy Josephson flux flow oscillator

Abstract

The current-voltage and spectral characteristics of a flux flow oscillator (FFO) based on a long Josephson junction are studied. The investigations are performed in the range of small bias currents and magnetic fields where the FFO radiates a quasi-chaotic signal with extremely large radiation linewidth, and the displaced linear slope (DLS) is observed at the current-voltage characteristic. Using direct numerical simulation of the sine-Gordon equation, it is shown that for large lengths of the Josephson junction or in the case of partial matching of the FFO with external waveguide system, the DLS with extremely large linewidth is transformed into Fiske steps with very narrow linewidth. As for Fiske steps, the appearance of regime of chaotic oscillations can be explained by multiple reflections of the traveling waves from junction ends rather than simply by excitation of the internal oscillation modes in the “soft” fluxon chain at weak magnetic fields.