A quasi-optical NbN HEB mixer with 800K DSB noise temperature at 2.5 THz

摘要

This paper presents the heterodyne measurement results of a quasi-optical NbN mixer at 2.5 THz. The HEB device was developed at LERMA in the frame of a CNES research project and the European programme Radionet FP7. It consists of a 2 μm wide, 0.2 urn long and about 3.5 nni thick NbN bridge on a silicon substrate. THz radiation is coupled to the HEB device through a quasi-optical circuit including an integrated spiral antenna and an anti-reflection coated hyper-hemispherical Si lens. The noise temperature measurement was performed at SRON using an optically pumped FIR gas laser as LO and a hot/cold load setup in vacuum to obtain the Y-factor. Two methods have been employed to measure the receiver noise temperature, either by adjusting the LO power at a fixed bias voltage between the hot and cold load to suppress the direct detection effect or by scanning the LO power when the bias voltage is kept constant to overcome the laser power fluctuations and the direct detection. The double sideband receiver noise temperatures obtained by both methods and without any corrections are as low as 800 K at 2.5 THz.