Optical Response of a Cold-Electron Bolometer Array Integrated in a 345-GHz Cross-Slot Antenna

Two series/parallel arrays of ten cold-electron bolometers with superconductor-insulator-normal tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. To increase the dynamic range of the receiver, all single bolometers in an array are connected in parallel for the microwave signal by capacitive coupling. To increase the output response, bolometers are connected in series for dc bias. With the measured voltage-to-temperature response of 8.8 μV/mK, absorber volume of 0.08 μm³, and output noise of about 10 nV/Hz^1/2, we estimated the dark electrical noise equivalent power (NEP) as NEP = 6 * 10^-18 W/Hz^1/2. The optical response down to NEP = 2 * 10^-17 W/Hz^1/2 was measured using a hot/cold load as a radiation source and a sample temperature down to 100 mK. The fluctuation sensitivity to the radiation source temperature is 1.3 * 10^-4 K/Hz^1/2. A dynamic range over 43 dB was measured using a backward-wave oscillator, a variable polarization grid attenuator, and cold filters/attenuators.