Abstract: The fluxon oscillators for producing electromagnetic radiation having a wavelength shorter than the shortest radio waves, but longer than the longest infrared radiation, may comprise two closely spaced superconductive ring-shaped members having a ring-shaped Josephson junction barrier therebetween capable of supporting the tunnelling of superconductive electrons across such barrier, a source of magnetic flux for initially producing at least one fluxon in the barrier, a power supply for producing an electrical biasing current between the superconductive members and across the barrier for causing movement of the fluxon along and around the ring-shaped barrier in a closed path, and a plurality of centers to produce enhanced superconductive electron current across the barrier, such centers being spaced around the ring-shaped barrier for causing cyclical variations in the velocity of the fluxon and thereby causing the radiation of electromagnetic energy at a frequency corresponding to the frequency of such cyclica