Abstract-3D direct writing of terahertz metamaterials based on TbFeO3 dielectric ceramics

Applied Physics Letters

Xinxi Zeng, Rong Wang, Xiaoqing Xi, Bo Li,  Ji Zhou

https://aip.scitation.org/doi/abs/10.1063/1.5035123

The integration of terahertz waves with metamaterials has become a key goal in modern photonics. In this work, we designed grating-structured metamaterials and face-centered-cubic (fcc) metamaterials based on TbFeO3 dielectric ceramics and built these materials using 3D direct writing technology. To simulate the behavior of the designed TbFeO3 metamaterials, the dielectric constant of TbFeO3 dielectric ceramic materials was determined. The desired strong electric and magnetic resonances were excited in the designed TbFeO3 metamaterials. The grating-structured metamaterials showed increased polarization-dependent transmittance as the line spacing decreased, while the fcc metamaterial showed a deep transmission dip at low frequencies and an electromagnetically induced increase in transmittance at higher frequencies. An increase in the electrical resistance contributed to the increase in the transmission properties of the fcc TbFeO3 metamaterial as its temperature decreased, while a reduction in the dielectric constant of TbFeO3 simultaneously caused a blueshift in this metamaterial. When combined with 3D direct writing technology, TbFeO3, with its high dielectric constant and low loss characteristics, represents an inexpensive and promising step towards the production of the next generation of low-cost, easy-to-fabricate, all-dielectric metamaterials.

Abstract-A Modularized and Switchable Component for Flexible Passive Device: Terahertz Photonic Crystals with Fine‐Tuning

Jiannan Gao, Rong Wang, Qian Zhao, Bo Li, Ji Zhou,




https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201800384?af=R

In this work, tunable terahertz photonic crystals (PCs) used as modularized and switchable components in flexible passive device are designed and prepared. Flexible woodpile structures created by the direct‐writing technology with a composite ink system composed of barium strontium titanate nanoparticles and polydimethylsiloxane are immersed in 5CB liquid crystals (LCs), where the orientation of LC molecule is modulated by the external magnetic field. Each of these can work in terahertz wavelength with specific position and depth of the dips in the transmittance spectra due to different geometries as well as having the ability of fine‐tuning. Experiments show that the photonic gaps of these PCs can cover from 0.2 to 0.3 THz, as well as about 7.5% fine tunability of photonic gap appearing with the orientation change of the magnetic field. More interestingly, the dips of photonic gaps keep the same position but become deeper with the increase of layer, an ability to realize another dimensional switchover. This work demonstrates that efficient terahertz PCs with different geometry parameters could be dynamically tuned by the orientation of magnetic field and it can open a universal approach to shrinking the size of device and rapid manufacturing in a large throughput.

Abstract-Experimental realization of Mie-resonance terahertz absorber by self-assembly method

Jiannan Gao, Chuwen Lan, Qian Zhao, Bo Li, and Ji Zhou

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-10-13001

Mie-resonance terahertz absorbers by self-assembly method are designed and demonstrated in experiments and simulations. A monolayer of zirconium dioxide (ZrO2) microspheres fixed on a copper film with designed grids that were manufactured by direct writing with a composite ink system composed of polydimethylsiloxane (PDMS). More importantly, different spacing and array configurations were created economically and efficiently, showing visual performance. Magnetic resonance leads to near-unity absorption at about 0.4 THz in the samples. This work demonstrates efficient terahertz absorbers and highlights a novel direct writing fabrication method that can be extended to produce other optical devices for applications.

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

Abstract-Dielectric meta-atom with tunable resonant frequency temperature coefficient

• Lingling Wu, 
• Xiaoqing Xi, 
• Bo Li & 
• Ji Zhou

https://www.nature.com/articles/s41598-017-02974-9

In this paper, we present a proof-of-concept of a new approach to achieving tailored resonant frequency temperature coefficients in dielectric meta-atoms. The technique involves introducing a thermally expanding or contracting material joining the active high permittivity dielectric absorbers. Both simulation and experiment show that by careful design of the element size and appropriate choice of thermomechanical intermediate layer material, increased or decreased resonant frequency shift temperature sensitivity is possible. Once the active dielectric material is chosen, and a meta-atom design determined, we show the resonant frequency shift depends on the thermal expansion coefficient of the intermediate layer. This work demonstrates the feasibility of manipulating the blue or red shift of metamaterial devices by introducing temperature responsive intermediate layers into meta-atoms.Furthermore, this method could also be applied in the Terahertz, infrared or even optical frequencies on scaled meta-atoms.

Abstract-Anisotropic terahertz dielectric responses of sodium nitrate crystal

Xiaojian Fu,   Youting Song,   Chang Qing Sun and   Ji Zhou  

Phys. Chem. Chem. Phys., 2014, Accepted Manuscript

DOI: 10.1039/C3CP55484H
Received 28 Dec 2013, Accepted 18 Feb 2014
First published online 18 Feb 2014
http://pubs.rsc.org/en/content/articlelanding/2014/cp/c3cp55484h#!divAbstract

Terahertz (THz) spectroscopy has become an effective tool to characterize the low-frequency rotational and vibrational modes of molecules. In addition, novel THz dielectric responses and optical properties on the basis of molecular rotation and vibration have attracted lots of attention because of their potential application in THz devices. In this paper, the dielectric response of low-symmetric sodium nitrate crystal in the frequency range of 0.2-1.5 THz was experimentally demonstrated. Four absorption bands at 0.23, 0.47, 0.92, and 1.15 THz were observed in the dielectric spectra and were tentatively ascribed to the rotational motion of nitrate ions. Based on the molecular rotation mechanism, the dielectric anisotropy and dielectric resonance of the crystal were discussed in detail.

Abstract-Indefinite by nature: from ultraviolet to terahertz

Jingbo Sun , Natalia M. Litchinitser , and Ji Zhou

ACS Photonics, Just Accepted Manuscript

DOI: 10.1021/ph4000983

Publication Date (Web): February 14, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/ph4000983?journalCode=apchd5

A class of strongly anisotropic materials having their principal elements of dielectric permittivity or magnetic permeability tensors of opposite signs, so-called indefinite or hyperbolic materials, has recently attracted a significant attention. These materials enabled such novel properties and potential applications as all-angle negative refraction, high density of states, and imaging beyond diffraction limit using a so-called hyperlens. While several studies identified a few examples of negative refractions in birefringence crystals existing in nature, a majority of optical materials with hyperbolic dispersion relations known to date are engineered composite materials, “metamaterials,” such as metal-dielectric subwavelength multilayered structures or metal nanowires in a dielectric matrix. In this paper, we investigate naturally existing hyperbolic materials with indefinite permittivity for a range of frequencies from terahertz to ultraviolet. These include graphite, MgB2, cuprate and ruthenate. Spectroscopic ellipsometry is used to characterize the dielectric properties of graphite and MgB2, and a fitting method based on reflectance spectra is used to determine the indefinite permittivity of the cuprate and ruthenate. Lastly, we discuss the mechanisms behind indefinite properties of these materials.

Abstract-Hyperbolic metamaterial based on anisotropic Mie-type resonance

   

 
                                                
Chuwen Lan, Ke Bi, Bo Li, Xiaohan Cui, Ji Zhou, and Qian Zhao  »View Author Affiliations

 http://www.opticsinfobase.org/DirectPDFAccess/39485C48-C2C1-9228-2B4472D09D9DE1EE_274791/oe-21-24-29592.pdf?da=1&id=274791&seq=0&mobile=yes
A hyperbolic metamaterial (MM) based on anisotropic Mie-type resonance is theoretically and experimentally demonstrated in microwave range. Based on the shape-dependent Mie-type resonance, metamaterials with indefinite permeability or permittivity parameters are designed by tailoring the isotropic particle into an anisotropic one. The flat lens consisting of anisotropic dielectric resonators has been designed, fabricated and tested. The experimental observation of refocusing and a plane wave with ominidirectional radiation directly verify the predicted properties, which confirm the potential application in negative index material and superlens. This work will also help to develop all-dielectric anisotropic MM devices such as 3D spatial power combination, cloak, and electromagnetic wave converter, etc.