A dual-polarization mid-infrared kinetic inductance detector with photon-noise-limited performance

The mid-infrared (MIR) regime carries rich information about planetary-atmosphere biosignatures and galaxy evolution while providing higher star-planet contrast ratios than the optical band. Advanced detectors employing diverse technologies are under development to enable MIR observations across ground-based, balloon-borne, and space platforms. We demonstrate the design, fabrication, and characterization of a superconducting dual-polarization kinetic inductance detector (KID) operating around 20 μm. The MIR KID is a lumped-element device comprising a tantalum interdigitated capacitor connected in parallel with an aluminum inductor. The inductor, which simultaneously functions as an absorber, captures signals in two orthogonal linear polarizations. In a photon-flux-integrated mode, the detector achieves photon-noise-limited performance for absorbed powers ≳1 fW, with a limiting noise equivalent power of 2.9 × 10−18 W/Hz at 300 Hz.