Abstract
Access to the transverse spin of light has unlocked new regimes in topological photonics. To achieve the transverse spin from 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 of each field experiences spatial inversion, which leads to a mismatch between the intensities of the field and its spin component and hinders the global observation of the transverse spin. Here, we reveal a globally pure transverse spin of the electric field in which the field intensity signifies the spin distribution. Starting from the target spin mode for the inverse design of required spatial profiles of anisotropic permittivities, we show that the elliptic-hyperbolic transition around the epsilon-near-zero permittivity allows for the global conservation of transverse spin handedness of the electric field across the topological interface between anisotropic metamaterials. Extending to the non-Hermitian regime, we develop annihilated transverse spin modes to cover the entire Poincaré sphere of the meridional plane. This result realizes the complete optical analogy of three-dimensional quantum spin states.
Highlights
Noticing that the spatial inversion of T spin originates from the transverse light confinement, we reveal that the globally unique handedness of T spin can be achieved by implementing a topological transition around the uniaxial epsilon-near-zero (ENZ) permittivity in the transverse coordinate
By inversely designing the landscapes of anisotropic permittivities according to the target spin wave profile, we demonstrate the construction of arbitrary profiles of T-spin modes [Figs. 1(f)–1(h)] including zero spin [Fig. 1(i)], which preserves the global spin purity
We focus on the transverse magnetic (TM, magnetic field Hz along the z axis) mode in the x-y plane, and it can be readily extended to the transverse electric (TE) mode with dual symmetry [19]
Summary
Noticing that the spatial inversion of T spin originates from the transverse light confinement, we reveal that the globally unique handedness of T spin can be achieved by implementing a topological transition around the uniaxial epsilon-near-zero (ENZ) permittivity in the transverse coordinate. By inversely designing the landscapes of anisotropic permittivities according to the target spin wave profile, we demonstrate the construction of arbitrary profiles of T-spin modes [Figs.
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