Multifunctional Device for Circular to Linear Polarization Conversion and Absorption

• Published in: Annalen der Physik 2023-07, Vol.535 (7), p.n/a
• Main Authors: Liao, Si‐yuan, Qiao, Zhen, Sui, Jun‐yang, Zhang, Hai‐feng
• Format: Article
• Language: English
• Subjects: Absorption spectra; Bandwidths; Circular polarization; Conversion; Electrical resistivity; Linear polarization; metastructures; multifunctional devices; Optical pumping; perfect absorption; polarization converters; Silicon; Ultrawideband; Wave reflection
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.202300195

In this paper, a metastructure multifunctional device for circular‐to‐linear polarization conversion (PC) and perfect absorption is proposed in which the electrical conductivity of the silicon material is controlled by light, thus changing the function of the device. The paper also explores three methods of optimizing bandwidth and their mechanisms, which are analyzed by means of current and energy density diagrams. The unit structure of this device adopts a 2 × 2 array, which is used for differentiated reflection of circular polarization waves, and forms linear polarization waves after reflection. In the other state, ultrawideband absorption can be achieved by changing the conductivity of silicon by external optical pumping, and the bandwidth is widened by inserting air resonators. In general, the device can form a PC at 0.89–1.31 THz with a relative bandwidth of 38% when there is no illumination. The resulting linear polarization wave has an axial ratio greater than 19 dB. When the silicon is excited by light resulting in a stable conductivity of around 9000 S m−1, the absorption band is 0.89–2.01 THz, the relative bandwidth is 77%, and the absorption rate is above 90%. This device can be used for communication, electromagnetic cloaking, and modulation. This paper presents an optical control‐based multifunction device that combines the functions of an absorber and a polarization converter, resulting in an ultra‐broadband absorption with an average absorptivity of 95.5% (relative bandwidth [RB] = 77%) at 0.89–2.01 THz or a polarization conversion from circular polarization to linear polarization waves (RB = 38%) at 0.89–1.31 THz.