Superconducting terahertz mixer using a transition-edge microbolometer

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We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition-edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and a rf signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (<0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (if) response. The mixer offers ≊4 GHz if bandwidth, ≊80 Ω rf resistive impedance, good match to the if amplifier, and requires only 1–20 nW of local oscillator power. The upper rf frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double-sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.