A 3.7 THz third-order distributed feedback quantum cascade laser as the local oscillator of a superconducting hot electron bolometer receiver

In this paper, we report on the investigation of a 3.7 THz phase-matched third-order distributed feedback (DFB) quantum cascade laser (QCL) as the local oscillator (LO) of a superconducting hot electron bolometer (HEB) heterodyne receiver. Due to the incorporation of the third-order Bragg gratings, the beam pattern of the QCL was found much improved. Beam pattern measurements show that the QCL has a narrow beam with ∼12×18 degree divergence, which is in good agreement with simulations by considering the gratings as an array of phased linear sources. Using this QCL as LO, we measured the noise temperature of a log-spiral antenna coupled superconducting HEB mixer at 3.7 THz. The lowest double-sideband (DSB) receiver noise temperature is about 4000 K, and reduced to 1100 K after correcting the optical losses. This result shows that phase-matched third-order DFB QCLs are very promising device as a LO in THz heterodyne receivers.