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Superoscillatory metalens for an azimuthally polarized wave with different orbital angular momentum

Light beams with helical phase-fronts are attractive for many optical applications, such as optical tweezers, particle manipulation, and other optical applications. A superoscillatory metalens has been designed for an azimuthally polarized wave at a wavelength λ  =  632.8  nm. Numerical simulation demonstrates that a superoscillation hollow dark spot is generated. The transverse inner FWHM is 0.358λ overcoming the diffraction limit, while the sidelobe ratio can be compressed to 18.3%. More importantly, for such incidence with different orbital angular momentum (OAM) l  =  1, 2, and 3, the proposed metalens also presents elegant subwavelength tight focusing performances (the FWHMs are 0.469λ, 0.352λ, and 0.737λ, respectively). Extensive investigations have been made to present the unique characteristics of the generated foci, the phase distribution patterns are given for different OAM values. Small size and ultrathin thickness make such lenses suitable for various optical applications.