Abstract-Gate-controlled terahertz focusing based on graphene-loaded metasurface

Naeem Ullah, Weiguang Liu, Guocui Wang, Zongyuan Wang, Ata Ur Rahman Khalid, Bin Hu, Juan Liu, and Yan Zhang

 (a) Schematic of the designed graphene-loaded metalens. A gate voltage Vg is applied to tune the chemical potential of graphene. (b) One unit-cell of the structure under the illumination of a linearly x-polarized THz wave. The transmitted y-polarized wave is dependent on both the C-shaped aperture and the graphene chemical potential. (c) 2-D illustration of a basic unit-cell, where P = 100µm, w = 10µm. The symmetric axis has an angle of β=45° to the x-axis.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-3-2789

Metasurfaces have proven their great application potentials in terahertz (THz) wave modulations. However, realizing an active metasurface retaining lensing functionality in the THz frequency regime is still highly desired. Here a metalens, featuring electrically tunable focal length, based on propagation phase delay, is proposed and demonstrated experimentally. To have full control over the designed lens functionality, a gold thin film etched with a C-shaped aperture antenna array covered by monolayer graphene is used. By applying a bias voltage to the graphene, the phase control of the antenna array is changed, and thus the focus of the linearly polarized THz beam can be flexibly tuned from 7.13mm to 8.25mm. The proposed approach has a promising perspective for a variety of applications in communication, reconfigurable flat optics and real-time imaging in THz regime.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Dynamical tuning of terahertz meta-lens assisted by graphene

Zongduo Huang, Bin Hu, Weiguang Liu, Juan Liu, and Yongtian Wang

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-34-9-1848

Metasurfaces, which are composed of arrays of scatters, can introduce abrupt change of optical properties. However, they lack flexibility to achieve active control. Here we propose a meta-lens with tunable focal length assisted by graphene at terahertz frequencies. The meta-lens consists of a monolayer graphene and a gold film etched with rectangle apertures with different lengths and rotation angles. By adjusting the gate voltage applied on the graphene layer uniformly, the chemical potential of graphene changes from 0.1 eV to 0.3 eV, and the focal length is changed by 1.25𝜆$1.25\lambda$ continually. This meta-lens is able to concentrate the terahertz beam to a spot size of one wavelength and the focal tuning mechanism works well at incident angles less than 40°.

© 2017 Optical Society of America