An ultra-broadband and highly-efficient tunable terahertz polarization converter based on composite metamaterial

A near perfect, ultra-broadband and highly-efficient terahertz reflective polarization converter based on multilayer metamaterial is proposed in this paper. The hybrid metamaterial unit structure consists of a split-ring metal pattern and a metal sheet separated by a dielectric resonator spacer. The polarization conversion ratio (PCR) is above 90% from 2.06 to 4.26 THz, with an optimal range between 2.98 and 4.16 THz where the efficiency is above 98% for normal incidence. It also shows excellent performance for oblique incidences. Moreover, the working band and the optimized frequency range for the polarization conversion can be manipulated by changing the open angle between the metallic arcs and the substrate thickness, respectively. Based on this design, two types of hybrid metamaterial converters are also investigated to swith off polarization conversion altogether or modify the polarization conversion bandwidth. A polarization converter with temperature controlled PCR is realized by adding a vanadium oxide (VO₂) mask on the designed structure. In addition, by integrating photoconductive silicon islands between the split-ring and metal bar a dual-band polarization converter can be realized. Combining with a polarizer, this window can act as an active THz filter.     

基于频率选择表面的双层改进型互补结构太赫兹带通滤波器研究

通过仿真计算和实验研究了一种基于频率选择表面的双层改进型互补结构太赫兹带通滤波器.对四裂缝互补型电感电容式谐振单元结构进行了改进,可以在提高滤波性能的同时增加单晶石英介质衬底的厚度.利用电磁仿真技术设计并加工了中心频率为0.28 THz的带通滤波器,并利用太赫兹时域光谱仪测试了在0.1—0.6 THz范围内此滤波器的传输频谱特性,实验结果与仿真结果基本一致.结果表明,利用双层改进型互补结构可以设计出对于入射角度不敏感、带外抑制佳、边带陡峭度大、能有效抑制寄生谐振的宽带太赫兹带通滤波器,并降低了加工难度.     

基于VO2薄膜相变原理的温控太赫兹超材料调制器

利用二氧化钒薄膜绝缘相–金属相的相变特性, 提出了一种基于超材料的温控太赫兹调制器, 研究了相变超材料在太赫兹波段的传输特性和温控可调谐特性. 当入射太赫兹波为水平偏振或垂直偏振状态时, 器件的透过率谱线在1 THz附近呈现出两个独立的、中心频率分别为1.3 THz和1.7 THz、 带宽分别为0.2 THz和0.35 THz的 透射宽带. 当温度从40℃至80℃变化时, 两宽带的透过率发生明显的降低, 在二氧化钒的相变温度(68℃)时尤其灵敏, 对入射光的二种偏振状态, 调制深度均达到60%以上, 实现了良好的调制效果. 关键词： 太赫兹超材料 2薄膜')" href="#">VO₂薄膜 调制器 相变     

An improved fishnet three-dimensional metamaterial with multiband left-handed characteristics at terahertz frequencies

We present the design of a multiband left-handed three-dimensional (3D) metamaterial based on improved fishnet structure at terahertz frequencies. The design realizes a three-dimensional material by mechanical stacking of multiple layers. The electromagnetic properties of the metamaterial have been investigated by numerical simulation. The results show that simultaneously negative values of permittivity, permeability and refractive index are found around the frequencies of 0.73, 0.85 and 1.12 THz for the electromagnetic wave normal incidence. The proposed metamaterial with independent polarization and compact effect offers a way to develop THz 3D materials and devices suitable for multifrequencies.     

Design and theoretical study of a polarization-insensitive multiband terahertz metamaterial bandpass filter

We report the design of a novel multiband metamaterial bandpass filter(BPF) in the terahertz(THz)-wave region. The designed BPF is composed of a metal–dielectric–metal sandwiched structure with three nested rings on the top surface and a cross structure on the bottom surface. Full-wave simulation results show that the designed BPF has three transmission peaks at frequencies of 0.42, 1.27, and 1.86 THz with transmission rates of-0.87,-1.85, and-1.83 d B, respectively.Multi-reflection interference theory is introduced to explain the transmission mechanism of the designed triple-band BPF.The theoretical transmission spectrum is in good agreement with the full-wave simulated results. The designed BPF can maintain a stable performance as the incident angle varies from 0?to 30?for both transverse electric and transverse magnetic polarizations of the incident wave. The designed BPF can be potentially used in THz devices due to its multiband transmissions, polarization insensitivity, and stable wide-angle response in the THz region.     

基于超材料的偏振不敏感太赫兹宽带吸波体设计

本文设计了一种基于超材料的偏振不敏感太赫兹宽带吸波体.吸波体包含两层金属和一层中间介质,表面金属层每一个周期单元由五种尺寸接近的金属块按照相邻不同的规律排列成5×5的方形阵列.各种尺寸金属块分别产生单峰谐振吸收,五个谐振吸收峰相互靠近从而产生宽带吸收.通过研究吸波体表面电流和电场z分量分布情况可知,入射太赫兹能量的吸收主要是由y方向上电场引起的电偶极子振荡和z方向上磁场引起的磁极化产生,而且金属层的欧姆损耗起主要作用.仿真结果表明,吸波体吸收率在80%以上的带宽约为1.2 THz,最高吸收率可达98.7%,半峰全宽(FWHM)为1.6 THz,该宽带吸波体的厚度约为中心波长的二十分之一,对偏振方向不敏感,且能实现大角度吸收,在太赫兹频段的电磁隐身、测辐射热探测器以及宽带通信等领域有潜在的应用价值.     

基于二氧化钒宽、窄带可切换的双功能超材料吸收器研究

本文提出了一种宽、窄带可切换的双功能超材料吸收器.在超材料吸收器的结构中,引入了相变材料二氧化钒(VO2),仅利用单个可切换超表面就能实现不同的功能,其不同功能之间的相互转换通过VO2绝缘态和金属态之间的可逆相变特性实现.当VO2处于金属态时,设计的结构可以看作一个超材料宽带吸收器.仿真结果表明,在1.55THz至2....     

Manipulating Nonlinear Photocurrent from Interlayer Coupling in Bilayer Metamaterials for Polarized Terahertz Generation

Polarized terahertz (THz) wave generation is of great significance for chiral and anisotropic sensing applications. However, how to manipulate amplitude, polarization, and ellipticity of the THz generation is still a fundamental challenge. Herein, polarized THz wave generation is achieved from a bilayer metamaterial consisting of T-shaped structure (TSS) and split resonator rings (SRRs) by combining Maxwell and hydrodynamic equations. The elliptically polarized THz wave can be synthetized directly from horizontally and vertically polarized THz components due to the orthogonal nonlinear photocurrents along the arm-directions of TSS and SRRs, respectively. Besides, the ellipticity and the orientation angle of the THz polarization ellipse can be modulated by the twist angle between the SRRs and TSS layers. The maximum ellipticity can reach 0.34 while the orientation angle is tunable from −0.45 to 0.48π by tuning the twist angle. This work proposes an interlayer coupling method for the polarized THz sources based on metamaterials in potential circular dichroism and chiral sensing applications.     

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate.The two switchable functions can be simply achieved by inserting a VO₂ film in the metamaterial design.Finite-difference time-domain(FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO₂ is at metal phase,and convert x-polarized wave to circularly polarized wave when ...     

Switchable terahertz polarization converter based on VO2 metamaterial

A switchable terahertz (THz) polarization converter based on vanadium dioxide (VO₂) metamaterial is proposed. It is a 5-layer structure which containing metal split-ring-resonator (SRR), the first polyimide (PI) spacer, VO₂ film, the second PI spacer, and metal grating. It is an array structure and the period in x and y directions is 100 μm. The performance is simulated by using finite integration technology. The simulation results show that, when the VO₂ is in insulating state, the device is a transmission polarization converter. The cross-linear polarization conversion can be realized in a broadband of 0.70 THz, and the polarization conversion rate (PCR) is higher than 99%. Under thermal stimulus, the VO₂ changes from insulating state to metallic state, and the device is a reflective polarization converter. The linear-to-circular polarization conversion can be successfully realized in a broadband of 0.50 THz, and the PCR is higher than 88%.     

Bilayer-fish-scale ultrabroad terahertz bandpass filter

A bilayer fish-scale metamaterial is experimentally demonstrated to function as a broad bandpass filter in the terahertz regime. The measured 3 dB-bandwidth for normal incidence is 1.13 THz with a high transmittance. The measured transmission spectrum is described well by a model based on an RLC circuit and multiple reflections. The filter is relatively insensitive to incidence angles up to 45°.     

A simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber

Ultra-broadband metamaterial absorbers have attracted considerable attention due to their great prospect for practical applications. These absorbers are usually stacked by many (no. <20) different shaped or sized subunits in a unit cell, making it quite troublesome to be fabricated. Simple design for ultra-broadband absorber is urgently necessary. Herein, we propose a simple design of ultra-broadband and polarization insensitive terahertz metamaterial absorber based on a double-layered composite structure on a metallic board, and each layer consists of two sets of different sized square metallic plates. Greater than 90 % absorption is obtained across a frequency range of 0.85 THz with the central frequency around 1.60 THz. The relative absorption bandwidth of the device is greatly improved to 53.3 %, which is much larger than previous results. The mechanism of the ultra-broadband absorber is attributed to the overlapping of four closely resonance frequencies. The proposed metamaterial absorber has potential applications in detection, imaging and stealth technology.     

太赫兹液晶材料与器件研究进展

液晶是一种性能优异的可调控光电功能材料,基于液晶的太赫兹器件有着广泛的应用前景,但高性能太赫兹功能器件的研发仍处于初级阶段.本文综述了太赫兹领域液晶材料与器件的研究现状,探讨了液晶技术与太赫兹技术相结合的发展趋势.     

Compact multiband left-handed metamaterial at terahertz frequencies

We design and analyze a novel multiband left-handed metamaterial based on a fishnet-like structure at terahertz (THz) frequencies.The metamaterial exhibits simultaneous negative refractions around the frequencies of 0.48,1.05,and 1.19 THz for the electromagnetic (EM) wave normal incidence,and around the frequencies of 0.20,0.79,and 1.13 THz for parallel incidence.The simulated results verify the left-handed properties.A particularly important observation is the capability of the proposed metamaterial with a single geometrical structure to display multifrequency operations in a unit cell.The compact metamaterial is a major step toward the miniaturization of THz materials and devices suitable for multifrequencies.     

Microelectromechanical systems bimaterial terahertz sensor with integrated metamaterial absorber

This Letter describes the fabrication of a microelectromechanical systems (MEMS) bimaterial terahertz (THz) sensor operating at 3.8 THz. The incident THz radiation is absorbed by a metamaterial structure integrated with the bimaterial. The absorber was designed with a resonant frequency matching the quantum cascade laser illumination source while simultaneously providing structural support, desired thermomechanical properties and optical readout access. Measurement showed that the fabricated absorber has nearly 90% absorption at 3.8 THz. A responsivity of 0.1°/μW and a time constant of 14 ms were observed. The use of metamaterial absorbers allows for tuning the sensor response to the desired frequency to achieve high sensitivity for potential THz imaging applications.     

基于石墨烯编码超构材料的太赫兹波束多功能动态调控

提出了一种基于石墨烯带的太赫兹波段的1 bit编码超构材料,可以实现太赫兹波束的数目、频率、幅度等参数多功能动态调控.该结构由金属薄膜、聚酰亚胺、硅、二氧化硅、石墨烯带组成.通过对石墨烯带施加两种不同的电压,可以实现一定频率范围内相位差接近180?的"0"和"1"数字编码单元,进而构成1 bit动态可控的编码超构材料.全波仿真结果表明,不同序列的编码超构材料能够实现波束数目从单波束、双波束、多波束到宽波束的调控.相同序列的编码超构材料,通过施加石墨烯带的不同电压能够实现宽频段波束频率的偏移.对于000000或者111111周期序列的编码超构材料,通过施加石墨烯带的不同电压还能够实现波束幅度的调控.因此这种基于石墨烯带的编码超构材料为灵活调控太赫兹波提供了一种新的途径,将在雷达隐身、成像、宽带通信等方面具有重要的意义.     

Design of a multiband terahertz perfect absorber

A thin-flexible multiband terahertz metamaterial absorber(MA) has been investigated. Each unit cell of the MA consists of a simple metal structure, which includes the top metal resonator ring and the bottom metallic ground plane,separated by a thin-flexible dielectric spacer. Finite-difference time domain simulation indicates that this MA can achieve over 99% absorption at frequencies of 1.50 THz, 3.33 THz, and 5.40 THz by properly assembling the sandwiched structure.However, because of its asymmetric structure, the MA is polarization-sensitive and can tune the absorptivity of the second absorption peak by changing the incident polarization angle. The effect of the error of the structural parameters on the absorption efficiency is also carefully analyzed in detail to guide the fabrication. Moreover, the proposed MA exhibits high refractive-index sensing sensitivity, which has potential applications in multi-wavelength sensing in the terahertz region.     

A multi-band and polarization-independent perfect absorber based on Dirac semimetals circles and semi-ellipses array

We design a four-band terahertz metamaterial absorber that relied on the block Dirac semi-metal(BDS). It is composed of a Dirac material layer, a gold reflecting layer, and a photonic crystal slab(PCS) medium layer. This structure achieved perfect absorption of over 97% at 4.06 THz, 6.15 THz, and 8.16 THz. The high absorption can be explained by the localized surface plasmon resonance(LSPR). And this conclusion can be proved by the detailed design of the surface structure. Moreover, the resonant frequency of the device can be dynamically tuned by changing the Fermi energy of the BDS. Due to the advantages such as high absorption, adjustable resonance, and anti-interference of incident angle and polarization mode, the Dirac semi-metal perfect absorber(DSPA) has great potential value in fields such as biochemical sensing, information communication, and nondestructive detection.     

Design of a type of broadband metamaterial absorber based on metal and graphene

In this paper, we demonstrate a kind of broadband metamaterial perfect absorber using both graphene and metal resonator elements. Through step by step design and simulation, wider absorption band from about 4.22 THz to 7.48 THz with average absorption rate up to 98.21% is achieved in the absorption spectrum. In addition, the absorber has characteristics of polarization insensitivity and wide incident angle due to its inherent rotational symmetry. Moreover, the absorption band can be adjusted by changing the chemical potential of the graphene. The superiorities of broadband, high absorption rate, polarization independent and wide-angle characteristics make it have potential application prospects in electromagnetic wave absorbing, signal sensing and detection, and other optoelectronic devices.     

Perfect metamaterial absorber design for solar cell applications

A new perfect metamaterial absorber based on metal-dielectric layer combination is designed and investigated to be used in solar cell application. The designed structure is particularly presented in the range of solar spectrum in order to utilize the solar energy effectively. Parametric studies with respect to the dimensions of the structure are carried out to characterize the absorber. According to the results, it is found that the metamaterial absorber has 99.99% absorption at 403.5 THz. In addition, the fractional bandwidth (FBW) of the absorption region is calculated and 22.2% FBW is obtained. Moreover the simulation results showed that the proposed design is also polarization and incident angle insensitive. As a result, the proposed metamaterial absorber provides perfect absorption for visible and near infrared frequency ranges and can be used for the realization of more efficient new solar cells.