4H-SiC-based polarization-multiplexed metalens balancing high NA and focusing efficiency in near-infrared bands

High-performance polarization-multiplexed metalenses (PMMs) hold remarkable transformative potential in optical platforms. However, balancing the numerical aperture (NA), focusing efficiency, and spectral bandwidth remains a significant challenge in the existing PMMs, thus restricting their extensive applications. To circumvent these challenges, we theoretically demonstrate two unique orthogonal (linear and circular) PMMs based on all 4H-silicon carbide (4H-SiC) with superior NA, sound focusing efficiency, and broad wavelength range. This is achieved by judiciously engineering stacked rectangular 4H-SiC pillars based on either the propagation phase or geometric phase. The results show that the linear PMM (LPMM) works well (i.e., focusing efficiency > 60%, NA > 0.658) at wavelengths spanning from 800 nm to 925 nm, whereas the circular PMM (CPMM) achieves parallel performances over a bandwidth of 775 nm-900 nm. More particularly, both the PMMs can achieve excellent features with high NA of 0.7, focusing efficiency exceeding 75%, and sub-diffraction focal spot size of around 607 nm at the operating wavelength of 850 nm. As a proof-of-principle demonstration, the well-designed LPMM and CPMM can be further leveraged to get access to high-capability polarization imaging and encryption.