Compact broadband fractal absorber for mid-infrared superconducting photon detectors

This work introduces a new architecture for Superconducting Nanowire Single-Photon Detectors (SNSPDs) specifically designed for efficient operation in the mid-infrared (3–7 μm) range. The design integrates a resonant plasmonic absorber with a fractal metasurface based on a Gosper curve to achieve broadband, polarization-insensitive absorption. A superconducting niobium nanowire serves both as the photon detector and plasmonic absorber. Combined with a reflective backplane and a thin dielectric spacer, the compact structure addresses the limitations of traditional optical cavities at longer wavelengths. The proposed approach offers a scalable solution for MIR photon detection with potential applications in thermal imaging, quantum sensing, and molecular spectroscopy.