Fig. 6: Tunable ring-cavity OAM source based on the unidirectional guided wave-driven metasurface.
From: Unidirectional guided-wave-driven metasurfaces for arbitrary wavefront control
a Schematic of a ring-cavity OAM source enabled by the unidirectional guided wave-driven metasurface. Unidirectional phase modulation provided by the metasurface intrinsically breaks the degeneracy of CW and CCW WGMs, leading to multiple OAM radiation at different frequencies. The dependence of USMP dispersion on geometric parameter and external magnetic field makes the radiated OAM modes tunable. b, c Numerical characterization of NΔφcl/2π from the ring-cavity OAM source with varied external magnetic field (H0) and dielectric depth (d) at different frequencies, the integer value of which corresponds to OAM with certain topological charge. d Simulated far-field phase (top), intensity (middle) and real part (bottom) profiles of the field component Er of generated beams tuned through external magnetic field (H0) corresponding to different OAM eigenstates, which are marked in (b). e The corresponding results of generated OAM beams with different eigenstates for different frequencies, which are marked in (c).
