Polarization-insensitive narrowband reflective wavefront manipulation through all-dielectric anisotropic subwavelength structures

Local metasurfaces provide high flexibility in shaping wavefronts but suffer from poor frequency selectivity. Here, we numerically present a reflective all-dielectric metasurface platform achieving simultaneous local phase control and spectral filtering: it reshapes the wavefront at a specific wavelength while spatially separating it from other wavelengths without requiring additional optics. The highly efficient phase control is inherently linked to the high polarization conversion ratio (PCR), ensured by a silicon nanoblock as a narrowband reflective half-wave plate through fundamental Mie resonances. The meta-atom exhibits near-unity peak reflection, a PCR reaching 0.97, and a quality factor around 20. By adjusting rotation angles, we disrupt the geometric phase conjugation, enabling polarization-insensitive applications, for example, a metalens with a high relative focusing efficiency (0.7) across the narrowband reflective spectrum. Our design exhibits high robustness against variations in the angle of incidence (up to 28°) and fabrication inaccuracies, allowing its implementation in various meta-applications.