Broadband switchable polarization-multiplexed metalens based on asymmetric spin-orbit interaction by using the composite phase metasurfaces

Ultrathin and flat metalenses exhibit distinct advantages in bandwidth performance and polarization control, owing to their advanced electromagnetic modulation capabilities. Recent researches have focused on multifunctional metalenses based on composite phase. However, these metalenses, typically designed for specific single or multiple-frequency responses, encounter challenges maintaining consistent performance across a broad spectrum. In this paper, we propose broadband polarization-multiplexed metalenses based on broadband asymmetric spin-orbit interaction using the composite phase control mechanism. The metalens can switch between different optical functions—from diffraction-limited focusing to super-diffraction focusing, or from a Bessel beam to a vortex beam—under illumination with left- or right-handed circularly polarized light across the wavelength range of 8 to 12 μm. The metalens possesses stable broadband phase control capabilities in the infrared atmospheric window. The proposed design method extends the bandwidth of polarization-multiplexed devices, making the metalens highly promising for super-resolution imaging, chirality detection, and holographic display applications.