Abstract-Efficient manipulations of circularly polarized terahertz waves with transmissive metasurfaces

Min Jia, Zhuo Wang, Heting Li, Xinke Wang, Weijie Luo, Shulin Sun, Yan Zhang, Qiong He, Lei Zhou,

Fig. 1: Working principle of the high-efficiency photonic spin Hall effect (PSHE) and background-free Bessel beam (BB) generation for circularly polarized (CP) waves in a transmission geometry.

https://www.nature.com/articles/s41377-019-0127-0

The unrestricted control of circularly polarized (CP) terahertz (THz) waves is important in science and applications, but conventional THz devices suffer from issues of bulky size and low efficiency. Although Pancharatnam–Berry (PB) metasurfaces have shown strong capabilities to control CP waves, transmission-mode PB devices realized in the THz regime are less efficient, limiting their applications in practice. Here, based on Jones matrix analysis, we design a tri-layer structure (thickness of ~λ/5) and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom (relative efficiency of ~90%) to build PB metadevices for manipulating CP THz waves. Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system. The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%, whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam. All the experimental results are in excellent agreement with full-wave simulations. Our results pave the way to freely manipulate CP THz beams, laying a solid basis for future applications such as biomolecular control and THz signal transportation.

Abstract-Angular dispersions in terahertz metasurfaces: Physics and applications

Meng Qiu, Min Jia, Shaojie Ma, Shulin Sun, Qiong He,  Lei Zhou,

https://journals.aps.org/prapplied/accepted/20070AedD5e1680fa1d60312978c2b8f3fcbaf4b7

Angular dispersion --- the response of a metasurface strongly depends on the impinging angle --- is an intrinsic property of metasurfaces, but its physical origin remains obscure which also hinders its applications in metasurface design. Here, we establish a theory to quantitatively describe such intriguing effects in metasurfaces, and verify it by both experiments and numerical simulations on a typical terahertz metasurface. The physical understanding gained motivates us to propose a new strategy to design meta-devices exhibiting impinging-angle-dependent multi-functionalities. As an illustration, we design a polarization-control meta-device that can behave as a half or quarter wave plate under different excitation angles. Our results not only reveal the physical origin of the angular dispersion, but also point out a new degree of freedom to manipulate light, which are important for designing meta-devices facing versatile application requests.

Abstract-Hybridization-induced broadband terahertz wave absorption with graphene metasurfaces

Nanli Mou, Shulin Sun, Hongxing Dong, Shaohua Dong, Qiong He, Lei Zhou, Long Zhang,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-9-11728

Electromagnetic (EM) wave absorption plays a vital role in photonics. While metasurfaces are proposed to absorb EM waves efficiently, most of them exhibit limited bandwidth and fixed functionalities. Here, we propose a broadband and tunable terahertz (THz) absorber based on a graphene-based metasurface, which is constructed by a single layer of closely patterned graphene concentric double rings and a metallic mirror separated by an ultrathin SiO2 layer. Plasmonic hybridization between two graphene rings significantly enlarges the absorption bandwidth, which can be further tuned by gating the graphene. Moreover, the specific design also makes our device insensitive to the incident angle and polarization state of impinging EM waves. Our results may inspire certain wave-modulation-related applications, such as THz imaging, smart absorber, tunable sensor, etc.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Ultra-wide band reflective metamaterial wave plates for terahertz waves

Shaojie Ma1, Xinke Wang2, Weijie Luo1, Shulin Sun3, Yan Zhang2, Qiong He1,4 and Lei Zhou1,4

Published 31 March 2017 • Copyright © EPLA, 2017 

http://iopscience.iop.org/article/10.1209/0295-5075/117/37007/meta

Terahertz (THz) electromagnetic waves have important applications in science and technology but available functional devices suffer from the issues of bulky size, low efficiency and narrow bandwidth. Here, based on Jones matrix and Poincaré sphere analyses, we present a set of general criterions to help design high-efficiency ultra-wide band THz wave plates using ultra-thin reflective metamaterials. Two half-wavelength and one quarter-wavelength THz wave plates are designed and fabricated based on the general criterions, and their excellent polarization manipulation capabilities are demonstrated experimentally. In particular, the realized devices, with thicknesses ~ λ/7, exhibit polarization-conversion efficiencies higher than 80% in ultra-wide working bandwidths (relative bandwidth >80% at about ~ 0.7 THz).