On and off-chip detection of radiation from HTS Josephson junction arrays

We have investigated the mutual phase interaction between a single detector junction and a phase-locked three-junction array of high-T-c Josephson junctions. The YBCO Josephson junctions were fabricated on a MgO bicrystal substrate. In the array junction structure, the de bias current was fed to the junction array having parallel geometry with each pair of junctions shunted by a superconducting coplanar microstrip superconducting loop. The configuration of bias leads was series connection of interlocking de SQUID's geometry which enables all junctions to oscillate at the same frequency. We measured the radiation power of a Josephson-junction array using an off-chip coupled to a radiometer and on-chip coupled to a single junction from centimeter- to millimeter-wave ranges. Clear self-induced Shapiro steps were observed in the current-voltage curves of the detector junction. The power transfered to the single detector junction was estimated from the modulation of Shapiro step height. The maximum detected power level was about 7 nW at frequency 150-250 GHz. The Josephson oscillation power excited the resonant mode coupled to the coplanar microstrip loops.