Abstract-Terahertz metasurface ultra-thin collimator for power enhancement

Takehito Suzuki, Kota Endo, and Satoshi Kondoh

(a) Terahertz metasurface ultra-thin collimator for power enhancement and (b) the design model of a single meta-atom extracted from the full structure assuming periodicity.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-15-22165

Manipulation of electromagnetic waves from radio to visible wavelengths could lead to technology to investigate unexplored wavebands. However, flexible control of terahertz waves is difficult, because few naturally occurring, appropriate materials and sophisticated optical components exist. We propose a 2.28-µm (0.02λ) ultra-thin terahertz metasurface collimator with a high directivity of 4.6 times (6.6 dB) consisting of 339 pairs of meta-atoms compared with a single terahertz continuous-wave source. The metasurface exhibits an extremely high refractive index of 15.0 and a low reflectance of 15.5% at 3.0 THz, and with Fresnel reflections for naturally occurring dielectric materials with high refractive indices avoided. This metasurface collimator should facilitate ground-breaking applications such as arbitrary phase converters, solid immersion lenses, and cloaking.

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

Abstract-Analytical model of terahertz metasurface for enhanced amplitude modulation

Jiawei Cong,Gaige Zheng, Zhiqiang Zhou,  Min Liu,   Mingyang Chen,  Hongbing Yao, Pengyu Wei,  Naifei Ren

http://iopscience.iop.org/article/10.1088/1361-6463/aad34d

Optically-driven terahertz (THz) modulation generally requires excitation of excessively large photoconductivity of active components, which poses huge challenges for realization and practical applications. With aid of an analytical circuit model, we demonstrate an approach to alleviate the trade-off between large amplitude modulation and use of low photoconductivity in complementary split-ring resonator modulators. As revealed by analytical results and verified by full-wave simulation, the maximum modulation depth and needed photoconductivity are determined by the inductance and gap resistance of the structure, respectively. Therefore, by tailoring its inductance and resistance via geometry adjustment, both improvement of modulation efficiency and reduction of photoconductivity are simultaneously realized. A large amplitude modulation ~0.5 is achieved with ultralow conductivity of 2000S/m. The proposed approach might offer a guideline for structure design of THz devices with various active components.

Abstract-Resonance coupling and polarization conversion in terahertz metasurfaces with twisted split-ring resonator pairs

Chenyu Li, Chun-Chieh Chang, Qingli Zhou, Cunlin Zhang, and Hou-Tong Chen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-21-25842

We investigate edge-coupling of twisted split-ring resonator (SRR) pairs in the terahertz (THz) frequency range. Using a simple coupled-resonator model we show that such a system exhibits resonance splitting and cross-polarization conversion. Numerical simulations and experimental measurements agree well with theoretical calculations, verifying the resonance splitting as a function of the coupling strength given by the SRR separation. We further show that a metal ground plane can be integrated to significantly enhance the resonance coupling, which enables the effective control of resonance splitting and the efficiency and bandwidth of the cross-polarization conversion. Our findings improve the fundamental understanding of metamaterials with a view of accomplishing metamaterial functionalities with enhanced performance, which is of great interest in realizing THz functional devices required in a variety of applications.

© 2017 Optical Society of America