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Josephson Flux-Flow Oscillators in
Microwave Fields
Mario Salerno
Mogens Samuelsen
ABSTRACT In this chapter we investigate, both analytically and numer-
ically, the flux-flow resonance oflong Josephson junctions in the presence
ofmicr owave fields. We consider the microwaves to be coupled to the junc-
tion both uniformly in space and through boundary conditions. Using a
perturbation analysis around the rotating background we derive analytical
expressions for the current-voltage characteristics. The dependence of the
flux-flow step on the amplitude ofthe rf-fieldand the appearance ofsatel-
lite steps are explained. As a result we find that for uniform microwave
fields the satellite steps are spaced around the main flux-flow resonance by
both odd and even harmonics of the rf-frequency, while for non-uniform
fields only the even harmonic satellites are present. These results are in
good agreement with direct numerical integration ofthe system.
1 Introduction
In the past years a great deal of interest have been devoted to the study
of the Josephson flux-flowoscillator, . a long Josephson junction oper-
ating in the flux-flowregime [1]-[10]. The interest in such a device resides
in its relatively high output power (of the order of µW at .4 - 1 THz)
[1, 7], wide bandwidth, and easy tunability, these being attractive features
for applications in superconducting millimeter-wave electronics [3, 5, 8, 9].
The flux-flowregime is achieved whena sufficiently large external mag-
netic field is applied to the junction so that an unidirectional motion of
fluxons, created at one edge and destroyed at the other, is generated. This
dynamics gives rise in the current-voltage (IV ) characteristics to an high
voltage step (flux-flowstep) split into a series of equally spaced Fiske [11]
substeps. Recently, an analytical description of these resonances in the ab-
sence of external microwave fields was provided [10]. On the othe