Propagation and generation of Josephson radiation in superconductor/insulator superlattices alternately containing two different barriers

The sine-Gordon equation for a Josephson coupled superconductor/insulator superlattice is derived using a Lagrangian formalism. This equation has essentially the same form as that given eariler by Kulik for a single Josephson junction but with different parameters. For the case of S/I superlattices alternately containing two different barrier thicknesses, the behavior of the propagation and generation of the Josephson radiation is governed by two coupled sine-Gordon equations, which results in two photon branches separated by a frequency gap. Some potential applications of these structures, involving increased outputs of the Josephson radiation and two hand filters, are discussed.