Design of an ultra-broadband achromatic metalens from the near- to short-wave infrared

Metalenses are crucial for miniaturized and highly integrated optical systems, yet their inherent chromatic dispersion restricts broader application. Although recent designs have improved achromatic performance, attaining ultra-broadband achromaticity across the near- and short-wave infrared spectra remains challenging, especially when reconciling processing feasibility with structural stability. In response to this challenge, a semi-embedded unit cell is proposed in this paper, which can effectively alleviate the trade-off between performance and fabrication feasibility. By simulating and analyzing a metalens with an aperture of 62µm and a focal length of 65 µm, we demonstrate that the proposed structure achieves achromatic focusing across the 1000-2400 nm wavelength range, even under oblique illumination with incident angles up to 23° (equivalent to a 46°field of view). Within the operating wavelength band, the focal plane shift of the metalens is limited to a maximum of 4.5%. It exhibits an average absolute focusing efficiency of 42.66%, a full width at half maximum (FWHM) close to the diffraction limit, and an average relative focusing efficiency of 49.65%. Additionally, the proposed metalens exhibits high robustness to variations in material properties and geometric parameters, maintaining stable performance under a refractive index tolerance of ±0.04, an embedded region height tolerance of ±5%, an exposed region height tolerance of ±3.75%, and a side length tolerance of ±4%. The proposed semi-embedded structure offers a novel and reliable approach for developing ultra-broadband metalenses, with strong potential for highly integrated imaging and on-chip photonic applications.