Terahertz dual-band polarization control and wavefront shaping over freestanding dielectric binary gratings with high efficiency. (August 2021)

• Record Type: Journal Article
• Authors: Yuan, Yiwu; Cheng, Jierong; Dong, Xipu; Fan, Fei; Wang, Xianghui; Chang, Shengjiang
• Is Part Of: Optics and lasers in engineering. Volume 143(2021)
• Publication Date: 2021-08
• Subjects: Metagratings -- Polarization manipulation -- Wavefront shaping -- Dual band -- 3D printing; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2021.106636
• Languages: English
• ISSNs: 0143-8166

Abstract

Abstract: Metasurfaces for multi-band or wideband polarization control are usually achieved by cascading or nesting several elements in a period, which complicate the structure and introduce crosstalk. In this work, independent polarization control is achieved around two terahertz frequencies, 0.14 THz and 0.3 THz, through a simple binary one-dimensional grating. The correlation of the phase retardation with frequency is broken, since it is determined by the propagation of a single mode at the lower frequency and by the interference of two modes at the higher frequency. Four gratings capable of different types of dual-band polarization control, a half-half wave plate, a half-quarter wave plate, a quarter-half wave plate and a quarter-quarter wave plate, are designed and experimentally tested. All the samples are made of polymers and 3D-printed as freestanding lightweight structures. The experimental results of all the samples validate polarization conversion with state-of-the-art high efficiency. Simulation results indicate their favorable bandwidth of more than 30%. The half-half wave plate gratings are further applied to build a metalens for efficient dual-band beam focusing based on the geometric phase. They show great potential in developing multifunctional terahertz elements using simple configurations.