Microwave analog of Stern-Gerlach effects using nonuniform chiral metamaterials

Abstract

This study observes microwave beam splitting dependent on circular polarizations through nonuniform chiral metamaterials. Nonuniform chiral metamaterials with a gradation in refractive index are constructed using chiral meta-atoms that exhibit optical activities at microwave frequencies. Microwave scattering far-field patterns by the nonuniform chiral metamaterials demonstrate a deflection of microwaves, which transmit in a direction perpendicular to the refractive index gradient. Furthermore, circularly polarized microwaves with opposite "spins of light" go their separate ways in the nonuniform chiral metamaterials. This phenomenon is an optical analog of the Stern-Gerlach effects for electrons.

Metamaterials with magnetism and chirality

“…spatial variation in the meta-atom or metamolecule density-in a direction perpendicular to the wave incident direction. The refractive index gradient due to the spatial variation deflects the center of gravity of the beam [29]. If the metamaterials consist of nonreciprocal MCh metamolecules, the bending direction depends on the beam propagation direction.…”

“…In this work, we have demonstrated that a metamolecule can boost MCh effects by several orders of magnitude compared to natural molecules. The enhanced and giant MCh effects thus open a door toward the realization of synthetic gauge fields [22][23][24][25][26][27][28][29]-for example, an effective magnetic field for electromagnetic waves. However, the values of nonreciprocal refractive index differences owing to the MCh effects by the single metamolecule were not yet large.…”

“…OA in optical systems is analogous to spin-orbit interaction in electronics, whereas the MO effect is to Zeeman splitting for electrons [29]. Even metamaterials solely with OA or the MO effect can be expected to contain rich physics.…”

“…Moreover, the quest for large optical MCh effects paves the way toward the realization of an effective magnetic field (i.e. synthetic gauge fields) [22][23][24][25][26][27][28][29], for electromagnetic waves. The MCh effect is, however, much weaker than the MO effect and OA in natural materials at room temperature.…”

Observation of asymmetric electromagnetic field profiles in chiral metamaterials

“…The present result provides an insight to the understanding of spin-orbit interaction of light. Last but not least, although implemented by microwave meta-atoms, the physical picture unveiled here applies to a broader class of artificial photonic structures in a wide range of frequencies from microwave [51] to visible light [52,53].…”