We designed and fabricated cyclic group symmetric metamaterials (CGSMs), anisotropic media showing an extrinsic optical orbital Hall effect. An exchange of angular momentum between spin and orbital angular momenta takes place in an optical beam propagating through anisotropic media such as plasmonic nanoantennas of concentric ring and tapered arc (TA) shape. In case of TA antenna an cross-polarized circular polarization scattered beam exhibits an extrinsic orbital Hall effect.
The CGSMs possess n-fold rotation symmetry and they are composed of plasmonic TA antennas. In case of circular polarization, the TA antennas effectively scatter incident light depending on the beam helicity. Both amplitude and phase gradients take place along the azimuthal direction for cross-polarized beams.
We used electron beam lithography to fabricate 30nm thick gold metamaterials patterned on borosilicate glass substrates. Six types of CGSMs with the symmetry order n from 1 to 6 were fabricated and measured. Each CSGM is composed of multiple TA antennas with the width varying from 45nm to 150nm organized in 8*n azimuthal segments of concentric rings repeated with 600nm radial spacing.
Measurements of orbital Hall transverse shifts of circularly polarized beams of right/left helicity were carried out at a wavelength of 1300nm. Because TA antennas are arranged in a metamaterial with a cyclic group n-fold rotation symmetry, the extrinsic orbital Hall transverse shifts from CGSM exhibit a geometrical pattern with the same symmetry. However, CGSMs with odd and even symmetry orders show a strongly contrasting difference in the character of transverse shifts. The observed geometrical patterns agree well with those obtained from FDTD theoretical simulation.
Yeon Ui Lee, Igor Ozerov, Frederic Bedu, Frederic Fages, and Jeong Weon Wu, "Extrinsic spin- and orbital-Hall effect in cyclic group symmetric metamaterial
(Conference Presentation)," Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 991818 (Presented at SPIE Nanoscience + Engineering: August 30, 2016; Published: 9 November 2016); https://doi.org/10.1117/12.2236798.5159106964001.
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