Millimeter-wavelength radiation from arrays of discrete high-temperature superconductor Josephson junctions

Josephson junction arrays could be competitive candidates for radiation sources in the frequency range from 0.5 to 1.5 THz. This is the range where compact solid-state continuous wave sources are most lacking. We investigated the millimeter-wave radiation from arrays of high-temperature superconductor bicrystal Josephson junctions embedded in a quasi-optical resonator. The novel approach of utilizing the intrinsic resonance modes of the substrate to improve the impedance coupling between the series array of discrete Josephson junctions and the quasi-optical resonator was investigated by experiments and electromagnetic field simulations. Radiation from the arrays containing up to 536 junctions was detected at about 80 GHz and liquid nitrogen temperature using a low-noise receiver. The detected maximum radiation power of the arrays was about 50 pW and the peak voltage agreed exactly with the Josephson current-voltage relation.