A photomixer local oscillator for a 630-GHz heterodyne receiver

A photomixer local oscillator (LO) operating at the 630-GHz difference frequency of two laser diodes was successfully demonstrated with a heterodyne detector based on a niobium superconducting tunnel junction. The low-temperature-grown GaAs photomixer generated 0.20 μW in the input spatial mode of the receiver. Using the photomixer LO, the double-sideband noise temperature of the receiver was 331 K-in good agreement with the 323 K noise temperature obtained when a multiplied Gunn oscillator generating 0.25 μW was substituted for the photomixer.