Intrinsic meron spin textures generated by an all-silicon terahertz meta-lens

Optical skyrmions and merons, topologically nontrivial textures of the electromagnetic field, have opened new avenues for structured light, yet their generation has so far relied on bulky focusing optics or specially crafted microstructures. Here we demonstrate that a planar all-silicon meta-lens can directly generate an intrinsic meron spin texture in a tightly focused terahertz beam at 0.9 THz. The meta-lens consists of half-wave-plate meta-atoms that simultaneously reverse the helicity of the incident circularly polarized wave and imprint a hyperbolic focusing phase through the propagation phase, yielding an effective numerical aperture of 0.8. Full-wave simulations show that the focused field carries a meron texture whose skyrmion number reaches ∓0.4915 at the meron radius for the two incident helicities, within two percent of the ideal half-integer value predicted by vectorial diffraction theory. The texture persists at three simulated frequencies spanning a fractional range of about eleven percent and, more strikingly, for fully polarized elliptical inputs away from the exact linear-polarization transition: the skyrmion number vanishes only for exactly linearly polarized input, which forms a measure-zero transition set on the equator of the Poincaré sphere, whereas its sign is selected by the spin content of the incident wave. These results establish a compact, broadband and polarization-tolerant terahertz platform for topological spin textures, with prospects for spin-controlled light-matter interaction, particle manipulation and topological optical information processing.