High‐Efficiency All‐Dielectric Metalenses for Mid‐Infrared Imaging

Abstract Metasurfaces‐based flat optics, which can make use of existing foundry planar technology for high‐throughput production, allows the arbitrary control of the wavefront and polarization of light within subwavelength thick structures. So far, however, flat optics for the mid‐infrared (MIR) has received far less attention than devices operating at visible or near‐infrared wavelengths. Here, polarization‐insensitive, highly efficient, all‐dielectric metalenses operating in the MIR around 4 µm are demonstrated. The metalens is designed using rigorous coupled‐wave analysis and is based on hydrogenated amorphous silicon (α‐Si:H) nanopillars supported by an MgF₂ substrate. The metalenses produce close to a diffraction‐limited focal spot and can resolve structures on the wavelength scale where the focusing efficiency reaches 78% at a magnification of 120×. The imaging qualities are comparable with commercial bulk‐molded chalcogenide aspheric lenses. These results provide novel solutions for existing MIR technology and nurture new functionalities with the population of miniaturized and planarized optoelectrical devices.