Incidence angle-dependent broadband chiral metamaterial for near-infrared light absorption

Abstract

The ability to spin-selectively absorb circularly polarized light (CPL) plays a critical role in various photonic devices. Here we propose and investigate a broadband chiral metamaterial composed of asymmetric split-ring resonators (SRRs), showing a wide spin-selective absorption band from 950 nm to 1200 nm with pronounced circular dichroism (CD) up to 20°. We demonstrate that the broadband absorption spectra originate from induced dual chiral resonance modes. Meanwhile, the two different resonances can be adjusted independently, suggesting great flexibility to the designed chiral absorption band for different purposes. Also, the chiralselective absorption performance is highly dependent on the oblique incident angle due to the extrinsic chirality. The chiral resonance modes can either be enhanced or destructed under oblique incidence. Such angle-dependent broadband chiral metamaterials may find potential applications for spin-orbit communications, chiral detection, polarimetric imaging, and biosensors.

Azimuth-Resolved Circular Dichroism of Metamaterials

“…In addition to intrinsic chirality in chiral geometric metamaterials, extrinsic chirality can also be induced for the metamaterials with nonchiral planar structures 23,28,29 when the incident light is oblique to the normal direction of the sample. In this case, a system composed of the wave vector of the oblique incident light and the achiral structure does not coincide with its mirror image, so this nonsuperimposable mirror symmetry of the system produces extrinsic chirality.…”

“…29,30 Extrinsic chirality has greater tunability, such as changing the angle of the incident light to the normal of the sample, the size of the sample, the symmetry of the unit structure, etc. 23,28,31 At the same time, the extrinsic chirality of the system can be modulated by the azimuth of metamaterials, and the magnitude and sign of CD caused by extrinsic chirality will also change accordingly. Here the azimuth refers to the angle between the direction of the sample symmetry axis and the direction of projection of the incident light on the sample surface.…”

“…In addition to intrinsic chirality in chiral geometric metamaterials, extrinsic chirality can also be induced for the metamaterials with nonchiral planar structures ,, when the incident light is oblique to the normal direction of the sample. In this case, a system composed of the wave vector of the oblique incident light and the achiral structure does not coincide with its mirror image, so this nonsuperimposable mirror symmetry of the system produces extrinsic chirality. , Extrinsic chirality has greater tunability, such as changing the angle of the incident light to the normal of the sample, the size of the sample, the symmetry of the unit structure, etc. ,, At the same time, the extrinsic chirality of the system can be modulated by the azimuth of metamaterials, and the magnitude and sign of CD caused by extrinsic chirality will also change accordingly. Here the azimuth refers to the angle between the direction of the sample symmetry axis and the direction of projection of the incident light on the sample surface.…”