A 3.5-THz, ×6-Harmonic, Single-Ended Schottky Diode Mixer for Frequency Stabilization of Quantum-Cascade Lasers

Efficient and compact frequency converters are essential for frequency stabilization of terahertz sources. In this article, we present a3.5-THz,× 6-harmonic, integrated Schottky diode mixer operating at room temperature. The designed frequency converter is based on a single-ended, planar Schottky diode with a submicron anode contact area defined on a suspended 2-μm ultra-thin gallium arsenide substrate. The dc-grounded anode pad was combined with the radio frequency E-plane probe, which resulted in an electrically compact circuit. At200-MHz intermediate frequency, a mixer conversion loss of about59dB is measured resulting in a40-dB signal-to-noise ratio for phase locking a3.5-THz quantum-cascade laser. Using a quasi-static diode model combined with electromagnetic simulations, good agreement with the measured results was obtained. Harmonic frequency converters without the need of cryogenic cooling will help in the realization of highly sensitive space and air-borne heterodyne receivers.