Abstract-Metal and graphene hybrid metasurface designed ultra-wideband terahertz absorbers with polarization and incident angle insensitivity

Nanoscale Advances

Lin Peng, Xiao-ming Li, Xiao Liu, Xing Jiang,  Si-min Li

https://pubs.rsc.org/en/content/articlepdf/2019/na/c8na00149a?page=search

Terahertz electromagnetic (EM) wave absorbers are vital in photonics, however, they suffer from limited bandwidth. A new approach for ultra-wideband (UWB) terahertz absorber design is proposed with metal and graphene metasurfaces. The UWB characteristics are owing to three factors: (1) the metal metasurface boosts the surface plasmon-polaritons (SPPs) of the graphene metasurface which leads to confined field enhancement, (2) the merging and interaction of the resonances of the metal and graphene metasurfaces, and (3) the multiple reflections and superpositions between the metasurfaces and the gold layer. A prototype designed using a dual-ring metal metasurface, fishnet graphene metasurface, polyimide substrate and gold reflecting layer is proposed. One cell of the prototype includes one metal dual-ring unit and four graphene fishnet units. The proposed absorber has an UWB bandwidth of 6.46 THz (145%) for absorptivity larger than 0.9, with a high octave of 6.21. The proposed absorber is also insensitive to the polarization state and incident angle of the illuminating EM waves. Besides, the amplitude modulation depth in the 5–6 THz band is up to 95.4%. The physical mechanisms of the wideband operation are also discussed. The research in this work could offer a new thought for UWB absorber design, and has potential applications in terahertz imaging, sensors, photodetectors and modulators 

Abstract-Multi-functional Device with Switchable Functions of Absorption and Polarization Conversion at Terahertz Range

Lin Peng, Xing Jiang, Si-min Li,

https://nanoscalereslett.springeropen.com/articles/10.1186/s11671-018-2811-z

Terahertz electromagnetic (EM) wave components usually have a single function, such as they can only convert the polarization state of an incident wave or absorb the incident energy, which would be a limitation for their applications. To make a breakthrough, a multi-functional device (MFD) is proposed in this paper, and it is capable of switching between absorption mode and polarization conversion mode. The device has a low-profile and simple structure, and it is constructed by graphene-based absorbing metasurface (AM) and gold-based polarization conversion metasurface (PCM). By controlling the chemical potential (μc) of the graphene, the leading role is transferred between the AM and the PCM, which leads to steerable absorption and polarization conversion (PC) modes. For the PC mode, the simulated polarization conversion ratio (PCR) is larger than 0.9 in the 2.11–3.63-THz band (53.0% at 2.87 THz). For the absorption mode, the simulated absorptivity is larger than 80% in the 1.59–4.54-THz band (96.4% at 3.06 THz). The physical mechanisms and operating characteristics of the MFD are discussed. This research has potential applications in terahertz imaging, sensors, photodetectors, and modulators.

Abstract-Tunable and multichannel terahertz perfect absorber due to Tamm surface plasmons with graphene

Xi Wang, Xing Jiang, Qi You, Jun Guo, Xiaoyu Dai, and Yuanjiang Xiang

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-6-536

In this paper, we have shown that perfect absorption at terahertz frequencies can be achieved by using a composite structure where graphene is coated on one-dimensional photonic crystal (1DPC) separated by a dielectric. Due to the excitation of optical Tamm states (OTSs) at the interface between the graphene and 1DPC, a strong absorption phenomenon occurs induced by the coupling of the incident light and OTSs. Although the perfect absorption produced by a metal–distributed Bragg reflector structure has been researched extensively, it is generally at a fixed frequency and not tunable. Here, we show that the perfect absorption at terahertz frequency not only can be tuned to different frequencies but also exhibits a high absorption over a wide angle range. In addition, the absorption of the proposed structure is insensitive to the polarization, and multichannel absorption can be realized by controlling the thickness of the top layer.

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