Abstract-Achromatic terahertz Airy beam generation with dielectric metasurfaces

 

Qingqing Cheng , Juncheng Wang, Ling Ma, Zhixiong Shen, Jing Zhang, Xiaoying Zheng ,Tao Chen, Ye Yu, Dong Yu, Qiong He, Wei Hu, Tao Li, Songlin Zhuang,  Lei Zhou

https://www.degruyter.com/view/journals/nanoph/ahead-of-print/article-10.1515-nanoph-2020-0536/article-10.1515-nanoph-2020-0536.xml?rskey=WV2s5h&result=7&tab_body=abstract

Airy beams exhibit intriguing properties such as nonspreading, self-bending, and self-healing and have attracted considerable recent interest because of their many potential applications in photonics, such as to beam focusing, light-sheet microscopy, and biomedical imaging. However, previous approaches to generate Airy beams using photonic structures have suffered from severe chromatic problems arising from strong frequency dispersion of the scatterers. Here, we design and fabricate a metasurface composed of silicon posts for the frequency range 0.4–0.8 THz in transmission mode, and we experimentally demonstrate achromatic Airy beams exhibiting autofocusing properties. We further show numerically that a generated achromatic Airy-beam-based metalens exhibits self-healing properties that are immune to scattering by particles and that it also possesses a larger depth of focus than a traditional metalens. Our results pave the way to the realization of flat photonic devices for applications to noninvasive biomedical imaging and light-sheet microscopy, and we provide a numerical demonstration of a device protocol.

Abstract-Broadband achromatic metalens in terahertz regime

Qingqing Cheng, Meilin Ma, Dong Yu, Zhixiong Shen, Jingya Xie, Juncheng Wang, Nianxi Xu, Hanming Guo, Wei Hu, Shuming Wang, Tao Li, Songlin Zhuang



https://www.sciencedirect.com/science/article/pii/S2095927319304621

Achromatic focusing is essential for broadband operation, which has recently been realized from visible to infrared wavelengths using a metasurface. Similarly, multi-terahertz functional devices can be encoded in a desired metasurface phase profile. However, metalenses suffer from larger chromatic aberrations because of the intrinsic dispersion of each unit element. Here, we propose an achromatic metalens with C-shaped unit elements working from 0.3 to 0.8 THz with a bandwidth of approximately 91% over the centre frequency. The designed metalens possesses a high working efficiency of more than 68% at the peak and a relatively high numerical aperture of 0.385. We further demonstrate the robustness of our C-shaped metalens, considering lateral shape deformations and deviations in the etching depth. Our metalens design opens an avenue for future applications of terahertz meta-devices in spectroscopy, time-of-flight tomography and hyperspectral imaging systems.

Abstract-Metamaterial-enhanced terahertz vibrational spectroscopy for thin film detection

Jingya Xie, Xi Zhu, Xiaofei Zang, Qingqing Cheng, Lin Chen, Yiming Zhu,

Fig. 1 Schematic illustration of (a) the experiment setup, (b) optical image of the metamaterial with L-tartaric acid deposited on it, and (c) the SRR unit cell.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-128&origin=search

We present metamaterial-enhanced terahertz vibrational spectroscopy to solve the low sensitivity problem of the THz ray absorption detection in molecular and biomolecular thin film. In a proof-of-principle experiment, we demonstrate the system in split ring resonators (SRRs) metamaterial that is strongly coupled to L-tartaric acid molecular under a low-temperature condition. The experimental results show that the extinction ratio of the detected signal can be significantly improved from 1.75 dB to 4.5 dB. The numerical calculations confirm and explain the experimental observations. By detuning the resonance of metamaterial, the behavior of the spectral signal is modified. When the SRRs and molecular vibrational resonance frequencies are closely aligned, a clear mode splitting is observed resulting in a transparency transmission with enhanced extinction ratio. This method shows great potential for application in thin film sensing by detecting molecular vibrations in the lower-energy terahertz region.

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

Abstract-Metasurface for multi-channel terahertz beam splitters and polarization rotators

XiaoFei Zang, HanHong Gong, Zhen Li, JingYa Xie, QingQing Cheng,   Lin Chen,   Alexander P. Shkurinov, YiMing Zhu, SongLin Zhuang,

https://aip.scitation.org/doi/abs/10.1063/1.5028401

Terahertz beam splitters and polarization rotators are two typical devices with wide applications ranging from terahertz communication to system integration. However, they are faced with severe challenges in manipulating THz waves in multiple channels, which is desirable for system integration and device miniaturization. Here, we propose a method to design ultra-thin multi-channel THz beam splitters and polarization rotators simultaneously. The reflected beams are divided into four beams with nearly the same density under illumination of linear-polarized THz waves, while the polarization of reflected beams in each channel is modulated with a rotation angle or invariable with respect to the incident THz waves, leading to the multi-channel polarization rotator (multiple polarization rotation in the reflective channels) and beam splitter, respectively. Reflective metasurfaces, created by patterning metal-rods with different orientations on a polyimide film, were fabricated and measured to demonstrate these characteristics. The proposed approach provides an efficient way of controlling polarization of THz waves in various channels, which significantly simplifies THz functional devices and the experimental system.

Abstract-Terahertz integrated device: high-Q silicon dielectric resonators

Jingya Xie, Xi Zhu, Xiaofei Zang, Qingqing Cheng, Lin Chen, and Yiming Zhu

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-1-50

We design, fabricate, and characterize the terahertz integrated resonators on the silicon platform. Based on mode analysis and selection, the high-Q feature of resonators made of low-loss high-resistivity Si material is achieved due to the excitation of the whispering gallery mode on waveguide-coupled single-mode racetrack rings and disk cavities. The experimental results demonstrate that the Q-factor can reach up to 2839 at 218.345 GHz, which is significantly improved compared with conventional THz cavities. These high Q-factor integrated resonators can be used as on-chip terahertz ultrasensitive sensors and as terahertz functional integrated circuits.

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