Heterodyne THz-wave receiver with a superconducting tunneling mixer driven by a high sweeping-speed photonics-based THz-wave local oscillator

We developed a broadband, highly sensitive heterodyne THz-wave receiver with a superconductor-insulator-superconductor (SIS) mixer. To fully utilize wide-bandwidth characteristics of the SIS mixer, we pump the SIS mixer with a photonics-based local oscillator (PLO) with fast frequency-sweeping speed. The received THz-wave signal down-converted to an intermediated frequency band is rapidly acquired by a high-speed analog-to-digital converter. The noise level of the developed receiver is equal to or smaller than twenty times the quantum-limited noise level between 225 and 425GHz. With this receiver, the frequency sweep from 225 to 475GHz with frequency resolution of 0.5GHz takes only about 2.5sec. Emission spectra of N2O gases measured with this receiver show its excellent performance.