Micromachined Tunable High‑Q Infrared Absorbers Enabled by Free-Standing All-Metallic Metasurfaces

Tunable narrowband infrared absorbers are appealing for various applications such as thermal emission control, optical sensing, and imaging. In this paper, we present a narrowband metasurface absorber for the long-infrared regime with a high quality factor and a wide tuning range mediated by integrating complementary metasurfaces with the Fabry–Perot cavity. The absorber features a tunable air spacer and a free-standing all-metallic metasurface membrane. The absorption response may be modulated by continuously altering the thickness of the air gap. The absence of lossy, dielectric spacer materials and the substrate substantially decreases the absorption bandwidth. The absorption performance in the band of 8.5–14 μm was theoretically analyzed using the corrected interference theory and experimentally demonstrated by a series of micromachined devices. We further constructed a micromachined, electrically tunable device for dynamic manipulation by integrating an electrostatic actuator to control the air gap. The implementation of the infrared absorber is fully compatible with the standard micromachining process, indicating a potential for mass production. Our design provides a promising platform for miniaturized, dynamic infrared metadevices.