Abstract-Multi-foci metalens for terahertz polarization detection

Ruoxing Wang, Jin Han, Jianlong Liu, Hao Tian, Weimin Sun, Li Li, and Xianzhong Chen

Schematic of the reflective THz multi-foci metalens for polarization detection. The ellipticity angle 𝜒$\chi$ and the direction of the major axis 𝛽$\beta$ of the incident and reflected polarization states are indicated in polarization ellipses.

https://www.osapublishing.org/ol/abstract.cfm?URI=ol-45-13-3506

We propose a reflective terahertz (THz) metalens with four focal points for polarization detection of THz beams. The metalens is composed of 𝑍$Z$-shaped resonators with spatially variant orientations, a reflective gold layer, and a dielectric spacer between them. The polarization states of the focal points include left circular polarization, right circular polarization, an incident polarization state, and a polarization state whose major axis is rotated 𝜋/4$\pi /4$ in comparison with that of the incident polarization. The handedness, ellipticity, and major axis of the polarization state can be determined based on the light intensities of the focal points. The uniqueness of the designed device renders this technique very attractive for applications in compact THz polarization detection and information processing.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Super terahertz phase shifter achieving high transmission and large modulation depth

Shuai Li, Jing Wang, Hao Tian, Li Li, Jianlong Liu, Guan Chao Wang, Jiaojiao Gao, Chengpeng Hu, and Zhongxiang Zhou

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-45-10-2834

We propose an industrial-grade liquid-crystal-based terahertz (THz) 2π-phase shifter with predictable ultra-high amplitude transmittance. The phase retardation reaches 360.5° at 1.68 THz by analyzing the birefringence of liquid crystal (LC), and the amplitude transmittance in 0.3–1.5 THz is over 83%. More than 91.5% transmittance can be reached by decreasing the scattering of the THz wave in the dynamic deflection process of LC molecules, and that is close to the transmittance limit of quartz-based devices. This millimeter-thick phase shifter reaches full phase modulation and ultra-high transmittance in a broad THz band, is easy to be integrated in a quasi-optical system with a compact size and can be utilized as a wave plate, even an element in a THz phased array.

© 2020 Optical Society of America

Abstract-Graphene/liquid crystal hybrid tuning terahertz perfect absorber

Ruoxing Wang, Li Li, Tong Guo, Tianzhi Wang, Jianlong Liu, Hao Tian, Fengjun Tian, and Weimin Sun

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-34-9406

We present, by simulations, a metastructured graphene/liquid crystal hybrid tuning terahertz perfect absorber that consists of graphene disk resonator arrays above a metallic layer separated with liquid crystal substrate. The liquid crystal refractive index and the graphene Fermi level are utilized to implement double-tuning operation to push the spectra scanning limit of the terahertz absorber. Our simulations demonstrate high performance of a near-linear broad tuning region and near-unity absorbance with wide incident angle and polarization independence. The range of the resonant frequency scan is notably enlarged at a spectral ratio of as high as Δ𝑓/𝑓=50%$\mathrm{\Delta }f/f=50\mathrm{\%}$ while ensuring absorbance beyond 90%. Such graphene/liquid crystal hybrid tuning scheme would be preferable to push the working-band limit of terahertz perfect absorbers.

© 2019 Optical Society of America

Abstract-Liquid crystal terahertz modulator with plasmon-induced transparency metamaterial

Jing Wang, Hao Tian, Yu Wang, Xueyan Li, Yujie Cao, Li Li, Jianlong Liu, Zhongxiang Zhou

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-5769

An electrically tunable terahertz (THz) modulator with large modulation depth and low insertion loss is performed with liquid crystal (LC) metamaterial. The modulation depth beyond 90% and insertion loss below 0.5 dB are achievable at normal incidence by exploiting plasmon-induced transparency (PIT) effect. The PIT spectra can be manipulated by actively controlling the interference between dipole mode and nonlocal surface-Bloch mode with LC. The incident angle tuning effect on PIT spectra shows that the large modulation depth and low insertion loss can remain over a wide range of working angles. The superior property and simplicity of design make this modulator promising in advanced terahertz communication.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Triple-band tunable perfect terahertz metamaterial absorber with liquid crystal

Ruoxing Wang, Li Li, Jianlong Liu, Fei Yan, Fengjun Tian, Hao Tian, Jianzhong Zhang,  Weimin Sun,

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32280

We report a compact triple-band tunable perfect terahertz metamaterial absorber (TMA) at the subwavelength scale of thickness, which is composed of a planar metallic disk resonator array above a conductive ground plane separated with liquid crystal (LC) mixture. The calculations of terahertz absorption spectra demonstrate triple near-unity absorption bands in the gap plasmonic resonance coupling regime. Three resonance frequencies of the absorber exhibit continuous linear-tunability as changing the refractive index of LC. Remarkably, each peak absorbance of the triple bands maintains at a level of beyond 99% in the whole tuning operation, and the absorbance can remain more than 90% over a wide range of incident angles. Our work suggests that the LC tunable absorber scheme has the potential to overcome the basic difficulty to perform simultaneously multiband spectral tuning and near-unity absorbance with wide angle of incidence and weak polarization dependence. The proposed LC-tunable multiband perfect TMA is promising in the application of biomolecular spectra-selective terahertz imaging and sensing.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing 

Abstract-Investigation of mechanism: spoof SPPs on periodically textured metal surface with pyramidal grooves

• Lili Tian
• , Jianlong Liu
• , Keya Zhou
• , Yang Gao
•  & Shutian Liu

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=4769349778953500837

In microwave and terahertz frequency band, a textured metal surface can support spoof surface plasmon polaritons (SSPPs). In this paper, we explore a SSPPs waveguide composed of a metal block with pyramidal grooves. Under the deep subwavelength condition, theoretical formulas for calculation of dispersion relations are derived based on the modal expansion method (MEM). Using the obtained formulas, a general analysis is given about the properties of the SSPPs in the waveguides with upright and downward pyramidal grooves. It is demonstrated that the SSPPs waveguides with upright pyramidal grooves give better field-confinement. Numerical simulations are used to check the theoretical analysis and show good agreement with the analytical results. In addition, the group velocity of the SSPPs propagating along the waveguide is explored and two structures are designed to show how to trap the SSPPs on the metal surface. The calculation methodology provided in this paper can also be used to deal with the SSPPs waveguides with irregular grooves.