Switchable ultra-broadband absorption and polarization conversion metastructure controlled by light

TLDR

The device is suitable for applications such as electromagnetic cloaking and communication. The study proposes a metastructure that switches between polarization conversion and absorption in the terahertz range via photoconductivity. Switching is achieved by varying silicon photoconductivity with light intensity, while broadband performance is enhanced by inserting air resonant cavities, locally varying dielectric thickness, and adding rectangular slots to the metal bottom plate. The device attains >90 % linear‑to‑linear polarization conversion over 0.96–1.47 THz (42 % bandwidth) and, at a fixed silicon conductivity of 3500 S/m, >90 % absorption over 0.75–1.73 THz (79 % bandwidth).

Abstract

This article proposed a metastructure device that can realize polarization conversion (PC) and absorption function switching in the terahertz (THz) range based on the photoconductivity effect. The photoconductance is formed by exposing silicon to different intensities of light, then the PC and absorption function can be switched. At the same time, the absorption bandwidth is expanded by inserting air resonant cavities into the dielectric substrate, changing the thickness of the dielectric locally, and cutting rectangular slots at the metal bottom plate. When the device works as a polarization converter, linear-to-linear PC with a polarization conversion rate of over 90% at 0.96-1.47 THz can be achieved, and its relative bandwidth is 42%. And when the silicon conductivity is fixed at 3500 S/m through illuminating, the device switches to an ultra-broadband absorber with over 90% absorption at 0.75-1.73 THz and a relative bandwidth of 79%. The designed device can be applied efficiently in many fields, such as electromagnetic cloaking and communication.