Wavelength-tuned transformation of the topological charge of a plasmonic vortex excited by linearly polarized light

Plasmonic vortex lenses (PVLs) have been developed to simplify the excitation conditions of surface plasmon polariton (SPP) vortex fields, transitioning from vector light with orbital angular momentum or circularly polarized light with spin angular momentum to linearly polarized (LP) light. However, these structures are typically designed for specific wavelengths. Even if they can operate at multiple wavelengths, it is impossible to alter the topological charge (TC) of the vortex by varying the wavelength. In this study, we propose a meta-atom, which can excite SPPs with varying phase delays when illuminated by LP light of the same polarization direction but at different wavelengths. By arranging these meta-atoms in various configurations on a chip, it becomes feasible to generate SPP vortices with distinct TCs under LP light at different wavelengths. This innovative, to the best of our knowledge, meta-atom offers a novel approach to designing a wavelength-multiplexing SPP vortex generator.