High Numerical Aperture Achromatic Meta‐Devices Through Dispersion Compensation

Abstract Dispersion engineering is a long‐standing challenge in optical systems, and it is particularly important for metasurfaces, which naturally suffer from strong chromatic aberrations due to their ultralow profile. Stacks of metasurfaces have recently implemented dispersion control to address these challenges. However, these approaches still suffer from bottlenecks in terms of the available material refractive index and aspect ratio, resulting in limited phase and group delay coverage, constraining their numerical aperture (NA), size, and operating bandwidth. To address these challenges, various ultra‐high NA dispersion‐tailored meta‐devices are explored using a proposed dispersion compensation strategy combined with full‐wave simulation‐free inverse design, instead of adopting large refractive index materials and high aspect ratio processing technology. Multiple meta‐devices with highly customized dispersion engineering are experimentally demonstrated, including broadband achromatic diffraction‐limited meta‐devices with NA = 0.98 and 60% fractional bandwidth. The proposed platform explores a paradigm for dispersion control via spatially cascaded metasurfaces, which may facilitate advanced and scalable dispersion functionalities of various dispersion control meta‐devices.