Microwave analog of Stern-Gerlach effects using nonuniform chiral metamaterials

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.

Figure 1

Dispersion relations in (a) chiral and (b) magneto-optical media. (c) A normal incidence to a medium with the refractive index gradient $n\left(x\right)$ in a direction perpendicular to the incident direction.

Figure 2

Schematics of (a) uniform and (b) nonuniform chiral metamaterials consisting of chiral meta-atoms.

Figure 3

Transmission amplitude spectra of uniform chiral metamaterials between 4.7 and 6 GHz at ${90}^{\circ }$. (a) Red and blue spectra correspond to microwaves received by a rectangle horn antenna in co- and cross-polarization configurations, respectively. (b) Green and yellow spectra correspond to microwaves received by LHCP and RHCP antennas, respectively.

Figure 4

Microwave scattering far-field patterns of uniform chiral metamaterials. Transmission amplitude is plotted as a function of rotation angle (horizontal axis) and frequency (vertical axis). Vertical broken lines indicate ${90}^{\circ }$. Microwaves are received by rectangle horn antenna in (a) co- and (b) cross-polarization configurations.

Figure 5

Microwave scattering far-field patterns of uniform chiral metamaterials received using (a) LHCP and (b) RHCP antennas. Transmission amplitude is plotted as a function of rotation angle (horizontal axis) and frequency (vertical axis). Vertical broken lines indicate ${90}^{\circ }$.

Figure 6

Microwave scattering far-field patterns of nonuniform chiral metamaterials received using LHCP [(a) and (c)] and RHCP [(b) and (d)] antennas. (a), (b) Density of chiral meta-atom is higher in ${180}^{\circ }$. (c), (d) Density of chiral meta-atom is higher in $0^{\circ }$.

Figure 7

Amplitude difference between transmitted microwaves measured by LHCP and RHCP antennas after uniform chiral metamaterial is plotted as a function of stage rotation angle (horizontal axis) and frequency (vertical axis). Red color corresponds to high transmission detected by LHCP antenna, while blue color corresponds to high transmission detected by RHCP antenna. Vertical broken line indicates ${90}^{\circ }$. Horizontal broken line indicates chiral resonance frequency of 5.2 GHz.

Figure 8

Amplitude difference pattern measured by LHCP and RHCP antennas after nonuniform chiral metamaterial is plotted as a function of angle (horizontal axis) and frequency (vertical axis). Meta-atoms concentrations are dense in the $0^{\circ }$ (a) and ${180}^{\circ }$ (b).