Transverse spinning of light with globally unique handedness

TL;DR

This paper demonstrates a method to achieve globally pure transverse spin in light waves, overcoming previous spatial inversion issues, by using inverse mode molding and epsilon-near-zero metamaterials, enabling full control of optical spin states.

Contribution

It introduces a novel approach to realize globally unique transverse spin in light through inverse eigenmode molding and topological interface engineering.

Findings

Achieved globally conserved transverse spin across metamaterial interfaces.

Extended the concept to non-Hermitian regimes with full Poincare sphere coverage.

Enabled complete transfer of optical energy to transverse spinning motions.

Abstract

Access to the transverse spin of light has unlocked new regimes in topological photonics and optomechanics. To achieve the transverse spin of nonzero longitudinal fields, various platforms that derive transversely confined waves based on focusing, interference, or evanescent waves have been suggested. Nonetheless, because of the transverse confinement inherently accompanying sign reversal of the field derivative, the resulting transverse spin handedness experiences spatial inversion, which leads to a mismatch between the densities of the wavefunction and its spin component and hinders the global observation of the transverse spin. Here, we reveal a globally pure transverse spin in which the wavefunction density signifies the spin distribution, by employing inverse molding of the eigenmode in the spin basis. Starting from the target spin profile, we analytically obtain the potential landscape and then show that the elliptic-hyperbolic transition around the epsilon-near-zero permittivity allows for the global conservation of transverse spin handedness across the topological interface between anisotropic metamaterials. Extending to the non-Hermitian regime, we also develop annihilated transverse spin modes to cover the entire Poincare sphere of the meridional plane. Our results enable the complete transfer of optical energy to transverse spinning motions and realize the classical analogy of 3-dimensional quantum spin states.