Abstract-Ultrathin freestanding terahertz vector beam generators with free phase modulation

 

Huixian Zhou, Jierong Cheng, Fei Fan, Xianghui Wang, Shengjiang Chang

Schematic of the bilayer metasurface for VBs’ generation. (b) and (c) show the structure in the top and bottom layers, respectively, where the discretized sectors and their symmetry axes are marked. (d) Schematic of the polarization conversion in each sector and the orientation of the metaatoms.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-2-1384&id=446364

Simultaneous control of phase and polarization offers a large degree of freedom to tailor the beam properties, for instance, enabling generation of structured beams such as vector beams and vector vortex beams. Here, we propose an ultrathin freestanding metasurface operating at the terahertz frequency for efficient generation of vector vortex beam with an arbitrarily defined topological charge from linearly polarized excitation. The metasurface is composed of bilayer metallic patterns separated by a thin quartz slab, with one layer determining the transmission polarization and the other controlling the transmission phase. The tightly cascaded two layers form a Fabry-Perot cavity to maximize the efficiency of the polarization and phase control. Two metasurfaces for generation of radially polarized vector beam with uniform phase and vortex phase are fabricated and tested at 0.14 THz. The experimental results successfully demonstrate the generation of high-quality vector beams with the desired phase. In the experiment, the ultrathin and freestanding properties allow the metasurface to be easily combined with other components, which shows great potential for the development of various compact terahertz systems.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Graphene metalenses with diverse electrical tunabilities at different terahertz frequencies

Huixian Zhou, Jierong Cheng, Fei Fan, Xianghui Wang, Shengjiang Chang,

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-59/issue-12/127106/Graphene-metalenses-with-diverse-electrical-tunabilities-at-different-terahertz-frequencies/10.1117/1.OE.59.12.127106.short?SSO=1

Graphene has attracted widespread attention in dynamic optoelectronic devices due to its tunable electrical and optical properties. But different modulation capabilities of the graphene-based designs at different frequencies are less studied. We study the electrical tunability of transmissive metalenses based on graphene when working at three frequencies 0.3, 1.25, and 2 THz, respectively. The constitutive meta-atoms are composed of graphene patches and metallic gratings for efficient phase shift in the orthogonal polarization. Although the conductivity of graphene is tunable at all the frequencies, responses of meta-atoms show weak and strong dependence on the Fermi level at the low and high frequencies, respectively. Therefore, the focal length of the metalens is not electrically tunable at 0.3 THz. In contrast, the metalenses designed at 1.25 and 2 THz show electrically adjustable focal lengths, and the tuning range of the focal length increases with frequency. The research here provides clear guidance for the design of graphene metalenses with different electrical tunabilities for a variety of application scenarios.

© 2020 Society of Photo-Optical Instrumentation Engineers (SPIE) 0091-3286/2020/$28.00 © 2020 SPIE