Fig. 1. (a) Schematic diagram of the plasmonic OAM waveguide; (b) cross-section of the OAM waveguide; (c) energy percentage of the radial polarization component E_r of the surface plasmon mode SP₁₁. Inset is the intensity distribution of the SP₁₁ mode.

Fig. 2. Intensity and phase distributions of SP₁₁^e, SP₁₁^o, SP_+1,1^OAM, and SP_−1,1^OAM modes.

Fig. 3. Mode properties of SP_+1,1^OAM mode in the nano-waveguides with r₃ − r₂ = 5 nm, r₄ − r₃ = r₂ − r₁, and r₅ − r₄ = 50 nm. (a) Modal effective index; (b) normalized mode area; (c) propagation length; (d) FoM. The inset is the cross-section of the OAM waveguide, where the thickness of the As₂S₃ layer is denoted as r₂ − r₁.

Fig. 4. (a) Normalized mode area and (b) FoM of SP_+1,1^OAM modes in the nano-waveguides with r₄ − r₃ = r₂ − r₁ = 10 nm and r₅ − r₄ = 50 nm. Inset in (b) denotes the thickness of SiO₂ layer as r₃ − r₂. (c) Normalized mode area and (d) FoM of SP_+1,1^OAM modes in the nano-waveguides with r₂ − r₁ = 10 nm, r₃ − r₂ = 5 nm, and r₅ − r₄ = 50 nm. Inset in (d) denotes the thickness of the outer As₂S₃ layer as r₄ − r₃.

Fig. 5. FoM of the SP_+1,1^OAM mode in four kinds of the nano-waveguides: the Ag nanowire (Model 1), the Ag nanotube (Model 2), the ring-core hybrid waveguide (Model 3), and this work.

Fig. 6. (a) Schematic diagram of the plasmonic OAM waveguide coupler. (b) Propagating electric field of the SP_+1,1^OAM mode coupler, where the white arrows represent the direction of optical energy flow. The upper dashed block diagram is the electric field and phase distribution of input SP_+1,1^OAM mode. The lower dashed block diagram is the electric field and phase distribution of coupling mode with the maximum coupling efficiency. (c) Coupling efficiencies of different modes in the SP_+1,1^OAM mode coupler. (d) Maximum coupling efficiency and corresponding coupling length of the SP_+1,1^OAM mode coupler with different center-to-center distances.

Fig. 7. Intensity and phase distributions of SP₂₁^e, SP₂₁^o, SP_+2,1^OAM, and SP_−2,1^OAM modes in the waveguide with r₁ = 150 nm.