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.