Josephson terahertz local oscillator

Voltage-tunable Josephson junction terahertz oscillators have been fabricated using rugged, high-current-density NbN/sub 1-x/C/sub x/ tunnel junctions with M O barriers. The radiation emitted from such junctions is detected on chip by a second Josephson junction which is capacitively coupled to the first. For oscillator junctions with a critical current density of J/sub c/ approximately 3.5*10/sup 4/ A/cm/sup 2/ the junction oscillates with a voltage amplitude of approximately=1.5 mV. The detected RF voltage level remain essentially constant from 300 GHz to above 1 THz, the upper limit of the detector. From measurements of the Josephson step height in the detector current-voltage characteristics, it is determined that the oscillator junction produces 0.5 mu W of terahertz radiation of which, due to impedance mismatch, 10 nW is coupled into the detector junction.>