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.