Josephson terahertz local oscillator

Voltage-tunable Josephson junction terahertz oscillators have been fabricated using rugged, high-current-density NbN_1-xC_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_c~3.5×10⁴ A/cm² the junction oscillates with a voltage amplitude of ≈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 μW of terahertz radiation of which, due to impedance mismatch, 10 nW is coupled into the detector junction