Achromatic generation of radially polarized beams in visible range using segmented subwavelength metal wire gratings

We propose an efficient method to achromatically transform a circularly polarized beam to a radially polarized beam in the visible range using segmented subwavelength metal wire gratings. We present a theoretical analysis of the relationship between the polarization purity of the transmitted beams and the number of segments. To verify our analysis, we fabricate a device composed of four quadrant sectors of subwavelength metal wire gratings and measure the transformation properties of the device at visible wavelengths of 488 nm, 532 nm, and 633 nm, which show a good agreement with theoretical results and the broadband achromatic property of the generation method.