Optimization of Bicrystal Josephson Junctions and Arrays in a Fabry-Perot Resonator

We report on the investigation of the coupling mechanism of a resonant millimeter wave electromagnetic field with bicrystal Josephson junction arrays embedded in a hemispherical Fabry-Perot resonator. We have found that our high-temperature superconductor array can be modeled as a thin film grid polarizer. In agreement with this model a strong dependence of the coupling of the Josephson junctions on the polarization of the electric field in the resonator was measured. Numerical field simulations confirm this model. According to this model, the dimension and interval of the grids and the dimension of the Josephson junctions are optimized by simulations and experiments. After optimized, a maximum Josephson voltage of 28 mV for an array of 182 bicrystal junctions at a temperature of 75 K and a frequency of 74.39 GHz was achieved for the first time. Our coupling method has a strong potential to be used up to terahertz frequencies.