Fig. 1. Schematic diagram and dispersion analysis of double-slots helical grating with or without depth modulation. Panels (a), (b), and (c) present the structural descriptions, dispersion curves, and field distributions of eigenmodes for the uniform grating. On the other hand, panels (d), (e), and (f) depict the structural descriptions, dispersion curves, and field distributions of eigenmodes for the modulated grating.

Fig. 2. Excitation of the chiral plasmons. (a) Coupler utilized for the transformation of coaxial modes into plasmonic modes. (b) Dispersion curves of mode M0 as the slot depth increases. (c) Field distribution of plasmonic transmission.

Fig. 3. Verification of the excitation of the chiral plasmons. Panels (a), (b), and (c) show the schematic diagrams, sampling results, and transmission characteristics of the uniform grating, while panels (d), (e), and (f) depict the schematic diagrams, sampling results, and transmission characteristics of the modulated grating.

Fig. 4. Generation of the vortex beams. (a), (b), (c), and (d) are radiation field distributions, far-field directivities, and mode purities of generated vortex beams in bands B1,B2, B3, and B4.

Fig. 5. Experimental setups and measured results. (a) Measured dispersion of the radiation waves from the vortex beam emitter. (b) Measured and theoretical beam scanning characteristics. (c) Measured and simulated transmission performances between two couplers. (d) Experimental setups. (e), (f), (g), and (h) are phase distributions of generated vortex beams in bands B1,B2, B3, and B4.