Xu Zhixiang, Ni Cheng, Cheng Yongzhi, Dong Linhui, Wu Ling
School of Information Science and Engineering, Wuhan University of Science and Technology, Wuhan 430081, China.
Engineering Research Center for Metallurgical Automation and Detecting Technology Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China.
Nanomaterials (Basel). 2023 Jun 12;13(12):1846. doi: 10.3390/nano13121846.
In this paper, a photo-excited metasurface (MS) based on hybrid patterned photoconductive silicon (Si) structures was proposed in the terahertz (THz) region, which can realize the tunable reflective circular polarization (CP) conversion and beam deflection effect at two frequencies independently. The unit cell of the proposed MS consists of a metal circular-ring (CR), Si ellipse-shaped-patch (ESP) and circular-double-split-ring (CDSR) structure, a middle dielectric substrate, and a bottom metal ground plane. By altering the external infrared-beam pumping power, it is possible to modify the electric conductivity of both the Si ESP and CDSR components. By varying the conductivity of the Si array in this manner, the proposed MS can achieve a reflective CP conversion efficiency that ranges from 0% to 96.6% at a lower frequency of 0.65 THz, and from 0% to 89.3% at a higher frequency of 1.37 THz. Furthermore, the corresponding modulation depth of this MS is as high as 96.6% and 89.3% at two distinct and independent frequencies, respectively. Moreover, at the lower and higher frequencies, the 2π phase shift can also be achieved by respectively rotating the oriented angle (α) of the Si ESP and CDSR structures. Finally, an MS supercell is constructed for the reflective CP beam deflection, and the efficiency is dynamically tuned from 0% to 99% at the two independent frequencies. Due to its excellent photo-excited response, the proposed MS may find potential applications in active functional THz wavefront devices, such as modulators, switches, and deflectors.
本文提出了一种基于混合图案化光电导硅（Si）结构的太赫兹（THz）光激发超表面（MS），它可以在两个频率上独立实现可调谐反射圆极化（CP）转换和光束偏转效应。所提出的MS的单元结构由一个金属圆环（CR）、Si椭圆形贴片（ESP）和圆形双分裂环（CDSR）结构、中间介电基板以及底部金属接地平面组成。通过改变外部红外光束的泵浦功率，可以改变Si ESP和CDSR组件的电导率。通过以这种方式改变Si阵列的电导率，所提出的MS在较低频率0.65 THz时可实现0%至96.6%的反射CP转换效率，在较高频率1.37 THz时可实现0%至89.3%的反射CP转换效率。此外，该MS在两个不同且独立的频率下相应的调制深度分别高达96.6%和89.3%。而且，在较低和较高频率下，分别通过旋转Si ESP和CDSR结构的取向角（α）也可以实现2π相移。最后，构建了一个用于反射CP光束偏转的MS超单元，其效率在两个独立频率下可动态调谐至0%至99%。由于其优异的光激发响应，所提出的MS可能在有源功能太赫兹波前器件中找到潜在应用，如调制器、开关和偏转器。
