A Superconducting Terahertz Flux-Flow Oscillator: Estimation of the Emission Power to Open Space

In this paper, we calculate power of electromagnetic wave emitted to open space by a terahertz (THz) source based on a Josephson flux-flow oscillator (FFO). The FFO is integrated with a transmitting slot antenna and a superconductor-insulator-superconductor (SIS) tunnel junction on a single chip, providing a frequency-tunable signal in a wide range of 200 - 700 GHz to open space. For non-calibrated power measurements, we used a highly sensitive silicon bolometer at 4.2 K. A small part of output FFO power is branched to the on-chip SIS-mixer and was estimated by absolute value by means of the Tien and Gordon photon-assisted tunneling theory. Using the absolute value, a calibrated power emitted to open space was estimated in the whole operating range. A power of from fractions to a few $\mu \mathrm{W}$ was obtained with a maximum of about $3 \mu \mathrm{W}$ at 330 GHz.