Angular dispersion-enabled dynamic metasurface for tunable reflective focusing.

Active metasurfaces have garnered significant attention due to their potential to replace conventional bulky optical systems, offering advantages in terms of reduced weight and compactness. In this study, we introduce the incident angle as a novel degree of freedom for controlling wavefront modulation in dielectric metasurfaces. By utilizing the angular dispersion of Mie resonances supported by a silicon ring disk, different reflective phases are modulated under varying incident angles. As a proof of concept, we numerically demonstrate a dynamic metalens whose reflective focal length is tuned by the incident angle. By balancing reflectivity and reflection phase through an intelligent approach, we demonstrate a metalens with a focal length that switches with the incident angle: 10 μm at 15° incident angle and 20 μm at 20° incident angle, achieving focusing efficiencies of approximately 13.5% and 18.13%, respectively. Continuous focal tuning, facilitated by progressive incident angle adjustments, is also spontaneously enabled by global coupling. Our design introduces a new degree of freedom for the dynamic control of metasurfaces and provides an approach in the development of portable zoom lenses.