Frequency multiplication using superconducting weak links

An investigation was made of the mechanism of generation of oscillation modes in a resonator excited by a Josephson point junction or bridge. On the basis of a system of Maxwell's equations and material equations in the Fokker–Planck approximation expressions were derived for the amplitudes of the fundamental-frequency harmonics and for the number of harmonics with comparable amplitudes. It was shown that with an appropriate choice of junction parameters and excitation frequency, the number of harmonics may be ~10³, the harmonics in this case falling within the optical band. Detailed experimental investigations were made of the nonlinear high-frequency properties of a superconducting niobium–niobium point junction in an external microwave field. Different operating conditions with frequency multiplication by the point junction were studied. Theory and experiment were compared. It was found that for frequency multiplication in the submillimeter band, a superconducting point junction operating under nonequilibrium conditions is potentially more useful than a conventional Josephson point junction.