Abstract-Ultrafast all-optical terahertz modulation based on an inverse-designed metasurface

 

Weibao He, Mingyu Tong, Zhongjie Xu, Yuze Hu, Xiang’ai Cheng, Tian Jiang, 

Structure chart of ultrafast all-optical terahertz modulation. (a) Schematic illustration of hybrid structure combining Ge film with inverse-designed metasurface at the pump light of 800 nm for terahertz modulation. (b) Processed inverse-designed metasurface structure without Ge film covering on the face. (c) Processed inverse-designed metasurface structure covering 200 nm thick Ge film on the face. The scale bar in the pictures is 50 μm.

https://www.osapublishing.org/prj/fulltext.cfm?uri=prj-9-6-1099&id=451405

Metasurface plays a key role in various terahertz metadevices, while the designed terahertz metasurface still lacks flexibility and variety. On the other hand, inverse design has drawn plenty of attention due to its flexibility and robustness in the application of photonics. This provides an excellent opportunity for metasurface design as well as the development of multifunctional, high-performance terahertz devices. In this work, we demonstrate that, for the first time, a terahertz metasurface supported by the electromagnetically induced transparency (EIT) effect can be constructed by inverse design, which combines the particle swarm optimization algorithm with the finite-difference time-domain method. Incorporating germanium (Ge) film with inverse-designed metasurface, an ultrafast EIT modulation on the picosecond scale has been experimentally verified. The experimental results suggest a feasibility to build the terahertz EIT effect in the metasurface through an optimization algorithm of inverse design. Furthermore, this method can be further utilized to design multifunctional and high-performance terahertz devices, which is hard to accomplish in a traditional metamaterial structure. In a word, our method not only provides a novel way to design an ultrafast all-optical terahertz modulator based on artificial metamaterials but also shows the potential applications of inverse design on the terahertz devices.

© 2021 Chinese Laser Press

Abstract-Terahertz Metaphotonic Devices: Ultrafast Frequency Shift of Electromagnetically Induced Transparency in Terahertz Metaphotonic Devices (Laser Photonics Rev. 14(3)/2020)

Yuze Hu, Tian Jiang, Hao Sun, Mingyu Tong, Jie You, Xin Zheng, Zhongjie Xu, Xiangai Cheng

https://onlinelibrary.wiley.com/doi/abs/10.1002/lpor.202070019

In article number 1900338 by Tian Jiang and co‐workers, the resonance frequency tuning of electromagnetically induced transparency (EIT) is achieved by molecularizing silicon‐hybrid metasurfaces. The cover image shows the structure, where an all‐optical switching approach is used to realize an ultrafast EIT frequency shift at the THz regime. The proposed concept endows metaphotonic devices with advanced functionalities, providing a new opportunity for the metasurface‐based applications, such as high‐speed wireless communications, multiband sensors.

Abstract-Ultrafast Terahertz Frequency and Phase Tuning by All‐Optical Molecularization of Metasurfaces

Yuze Hu  Tian Jiang  Junhu Zhou  Hao Hao,  Hao Sun,  Hao Ouyang, Mingyu Tong, Yuxiang Tang, Han Li, Jie You, Xin Zheng,  Zhongjie Xu, Xiangai Cheng,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201901050

The integration of photoactive semiconductors exhibiting strong light–matter interactions into functional unit meta‐atoms facilitates effective approaches to dynamically manipulate terahertz (THz) waves. Here, a new metaphotonic modulator is proposed and comprehensively studied, which demonstrates extensive tunability of the resonant frequency and phase with the merit of ultrafast photoswitching. Specifically, parallel silicon (Si) bridges are embedded in metasurfaces to reinforce the connection ability, achieving ultrafast optical molecularization from a magnetic quadrupole into an electric dipole. Under femtosecond pulse excitation, the demonstrated resonant frequency tuning range is as high as 40% (from 1.16 to 0.7 THz) and can be further promoted up to 48% (from 1.56 to 0.81 THz) by varying the Si bridge length. Meanwhile, the phase delay at given frequencies can be controlled up to 53.3° without significantly changing the high transmission. Furthermore, the transient frequency switching and phase shifting dynamics are systematically investigated for the first time, showing a full recovery time within 2 ns. By optically molecularizing metasurfaces, extended tuning ranges with regard to the resonant frequency and phase, as well as an ultrafast switching speed, are simultaneously acquired in the proposed metamodulator, which provides deeper insight into the multifunctional active‐tuning systems

Abstract-Dielectric properties of a CsPbBr3 quantum dot solution in the terahertz region

Dongsheng Yang, Xiangai Cheng, Yu Liu, Chao Shen, Zhongjie Xu, Xin Zheng, and Tian Jiang

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-56-10-2878

In recent years, CsPbBr3${\mathrm{CsPbBr}}_3$ quantum dots (QDs) have attracted much attention due to their bright prospects in solar cell studies. Dielectric properties are important for the fabrication of optoelectronic devices. Here, the dielectric properties of a CsPbBr3${\mathrm{CsPbBr}}_3$ QD solution are investigated between 0.1 and 2.0 THz by terahertz time-domain spectroscopy. The measured frequency-dependent transmitted ratio is found to decrease from 0.96 to 0.80 in this range. By comparing different concentrations of the QD solution, the frequency-averaged absorption is linearly increased with the increase in QD concentration. After that, the frequency-dependent dielectric constant, including the complex refractive index, complex dielectric constant, and conductivity, is extracted by Fourier transform of the time-domain spectrum. An effective medium approach method is adopted to extract the complex dielectric constant of a CsPbBr3${\mathrm{CsPbBr}}_3$ QD inclusion, and a slight peak around 0.4 THz is found in the imaginary part of the dielectric constant. The result of Drude–Lorentz fitting shows that the phonon plays a dominant role in the dielectric properties of a CsPbBr3${\mathrm{CsPbBr}}_3$ QD solution. Moreover, the THz response of a CsPbBr3${\mathrm{CsPbBr}}_3$ QD is found to be unchanged when the test is conducted under illumination. We attribute this phenomenon to the discrete energy level of excitons in CsPbBr3${\mathrm{CsPbBr}}_3$ QDs due to quantum confinement, and design a comparative experiment to validate it. This study is significant for its deeper insight into the dielectric properties of CsPbBr3${\mathrm{CsPbBr}}_3$ QDs, and thus is helpful through its applications in optoelectronics.

© 2017 Optical Society of America