Topology‐Induced Phase Transitions in Spin‐Orbit Photonics

Abstract

Spin‐controlled vortex generation and spin‐Hall effect, two distinct effects discovered in optics, have been extensively studied recently. However, while physical origins of two effects are both due to spin‐orbit interactions, their inherent connections remain obscure which also hinders further explorations on the manipulations of them. Here, in studying the scattering of a spin‐polarized light beam at sharp interfaces, an intriguing phase transition between vortex generation and spin‐Hall shift trigged by varying the incidence angle is revealed. After reflection/refraction, the beam contains two components: normal and abnormal modes acquiring spin‐redirection‐Berry phases and Pancharatnam–Berry phases, respectively. Inside the abnormal beam, two classes of wave components gain Pancharatnam–Berry phases with distinct topological natures, generating intrinsic and extrinsic orbital angular momenta (OAM), respectively. Enlarging incidence angle changes the relative portions of these two contributions, making the abnormal beam undergo a phase transition from vortex generation to spin‐Hall shift. Such intriguing effect is experimentally observed at a purposely designed metamaterial slab, exhibiting efficiency enhanced by several‐thousand times compared to that at a conventional slab. These findings unify two previously discovered effects in a single framework, reinterpret previous results with clearer pictures, and shed light on understanding other physical effects involving the competition between intrinsic and extrinsic OAM.

Reaching the highest efficiency of spin Hall effect of light in the near-infrared using all-dielectric metasurfaces

“…This rectangular nanorod is known to induce a Pancharatnam–Berry phase 25 , 52 under normal incidence. However, the phase contributes negligibly to the SHEL because the Pancharatnam-Berry phase is more dominant than the spin-redirection phase only under normal incidence and at a close vicinity of it 50 ( θ i ≪ 1°), which is not where we are interested in. Hydrogenated amorphous silicon (a-Si:H) 53 is used for its high refractive index and low optical losses (Supplementary Note 7) .…”

“…Equation ( 1 ) is valid under condition of for a beam waist w , which is true except for a tightly confined beam under near-normal incidence ( θ i ≪ 1°). This narrow angular regime is where a transition from the SHEL to vortex generation occurs 50 and is out of our consideration.…”

Classical and generalized geometric phase in electromagnetic metasurfaces

“…Additionally, an intriguing phase transition between vortex generation and spin Hall shift triggered by varying the incidence angle is revealed. After reflection/refraction of a spin-polarized light beam at sharp interfaces, the beam contains two components: normal and abnormal modes acquiring spin-redirection Berry phases and PB phases, respectively [125] . Efficiency enhancement by several-thousand times compared to that at a conventional slab was observed at a purposely designed metamaterial slab.…”

Intrinsic Vortex–Antivortex Interaction of Light

“…[ 20–25 ] The orbital angular momentum Hall effect manifests the IOAM‐EOAM interaction. [ 13 ] We note that all these interaction processes should be mediated by optical matters [ 12,18,26 ] or take place under nonparaxial condition (e.g., the light is tightly focused [ 27 ] ). The process we are dealing with, however, is contrary to those processes.…”