Tunable circular dichroism created by surface plasmons in bilayer twisted tetramer nanostructure arrays

The optical chirality of a bilayer twisted tetramer nanostructure is investigated theoretically. The difference of transmission spectra under left- and right-handed circularly polarized extinction produces very large optical chirality of 91% due to the different plasmonic hybridization patterns between the nanorods. This structure also allows the generation of a perfectly right/left-handed system at certain modes, because this mode nearly vanishes under the illumination of the left/right-handed light. Moreover, tunable optical chirality is achieved, which is also found to be easily affected by geometric parameters such as the separation distance between the two layers, the length of the nanorod, and the arrangement of nanorods. We consider the charge vibrations of four nanorods at the same layer as an equivalent dipole and explain the dependence of the circular dichroic spectrum on the geometric parameters. This work suggests that the bilayer twisted tetramer nanostructure can be considered a potential candidate for achieving large optical chirality, applicable to the fields of polarization polarizer fabrication and biological detection.