Fig. 1. (a) Schematic illustration of a patterned twisted LC cell and its function as an achromatic OV generator. (b) Wavelength-dependent CP conversion efficiency of an optimized structure and polarization evolutions of different wavelengths on the Poincaré sphere. The wavelength range from 440 to 660 nm is considered and the evolution trajectories of three typical wavelengths, 450 nm (blue), 530 nm (green), and 630 nm (red), are presented. Dashed and solid lines reveal the trajectories before and after backtracking. Input polarization on the north pole and output polarization around the south pole are exhibited as insets.

Fig. 2. Polychromatic OV generation based on a self-phase compensated q-plate. (a) Phase diagram and (b) micrograph of the q-plate with q=0.5. (c) Optical setup for the OV characterization. P, polarizer; AQWP, achromatic quarter-wave plate; BS, beam splitter. (d) Corresponding polychromatic OVs and OAM detections.

Fig. 3. (a) Vector beams generated by the self-phase compensated q-plate with q=0.5 for LP incidence. Vector beams detected with an analyzer (b) crossed and (c) parallel to the polarizer. White and yellow arrows denote the directions of polarizer and analyzer, respectively. The incident wavelengths are labeled correspondingly.

Fig. 4. (a) Illustration of the dual-twisted LC configuration. (b) Phase diagram and (c) micrograph of a dual-twisted FPG with m=2. (d) Simulated (solid line) and detected (dots) wavelength-dependent diffraction efficiencies. Insets reveal the generated donut OVs of wavelengths the same as the dots marked in the same color and the insert dash rectangles present the astigmatic transformation results of the 650-nm OVs.