Focusing zone plate based on subwavelength grating

We designed, fabricated, and characterized a thin metalens that is capable of simultaneously manipulating the state of polarization and phase of incident light. The lens was manufactured in an amorphous silicon film of diameter 30 μm and has focal length of 633 nm. The lens converts a linearly polarized beam with wavelength of 633 nm into radially polarized light and produces a subwavelength focus whose size at full-width half-maximum intensity is 0.49λ and 0.55λ (λ is incident wavelength). The experimental results are in good agreement with the numerical simulation, with the simulated focal spot measuring 0.46λ and 0.52λ.