Electrically tunable resonant terahertz transmission in subwavelength hole arrays

An actively enhanced resonant transmission in a plasmonic array of subwavelength holes is demonstrated by use of terahertz time-domain spectroscopy. By connecting this two-dimensional element into an electrical circuit, tunable resonance enhancement is observed in arrays made from good and relatively poor metals. The tunable feature is attributed to the nonlinear electric response of the periodic hole array film, which is confirmed by its voltage-current behavior. This finding could lead to a unique route to active plasmonic devices, such as tunable filters, spatial modulators, and integrated terahertz optoelectronic components.

Effect of external electric field on the terahertz transmission characteristics of electrolyte solutions

We fabricated a microfluidic chip with simple structure and good sealing performance,and studied the influence of the electric field on THz absorption intensity of liquid samples treated at different times by using THz time domain spectroscopy system.The tested liquids were deionised water and CuSO_(4),CuC_(l2),NaHCO_(3),Na_(2)CO_(3) and NaCl solutions.The transmission intensity of the THz wave increases as the standing time of the electrolyte solution in the electric field increases.The applied electric field alters the dipole moment of water molecules in the electrolyte solution,which affects the vibration and rotation of the whole water molecules,breaks the hydrogen bonds in the water,increases the number of single water molecules and leads to the enhancement of the THz transmission spectrum.

Extraordinary terahertz transmission through subwavelength spindle-like apertures in NbN film

We studied numerically the temperature dependent extraordinary terahertz transmission through niobium nitride(NbN) film perforated with subwavelength spindle-like apertures. Both the resonant frequency and intensity of extraordinary terahertz transmission peaks can be greatly modified by the transition of NbN film from the normal state to the superconducting state. An enhancement of the(±1, 0) NbN/magnesium oxide(MgO) peak intensity as high as 200% is demonstrated due to the combined contribution of both the superconducting transition and the excitation of localized surface plasmons(LSPs) around the apertures. The extraordinary terahertz transmission through spindle-like hole arrays patterned on the NbN film can pave the way for us to explore novel active tuning devices.

Transmission characteristics of terahertz Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab

The transmission of terahertz(THz)Bessel vortex beams through a multi-layered anisotropic magnetized plasma slab is investigated by using a hybrid method of cylindrical vector wave functions(CVWFs)and Fourier transform.On the basis of the electromagnetic boundary conditions on each interface,a cascade form of expansion coefficients of the reflected and transmitted fields is obtained.Taking a double Gaussian distribution of the plasma density as an example,the influences of the applied magnetic field,the incident angle and polarization mode of the incident beams on the magnitude,OAM mode and polarization of the transmitted beams are analyzed in detail.The results indicate that the applied magnetic field has a major effect upon the polarization state of the transmitted fields but not upon the transmitted OAM spectrum.The incident angle has a powerful influence upon both the amplitude profile and the OAM spectrum of the transmitted beam.Furthermore,for multiple coaxial vortex beams,an increase of the maximum value of the plasma density causes more remarkable distortion of both the profile and OAM spectrum of the transmitted beam.This research makes a stable foundation for the THz OAM multiplexing/demultiplexing technology in a magnetized plasma environment.

Dynamically controlled asymmetric transmission of linearly polarized waves in VO_(2)-integrated Dirac semimetal metamaterials

We numerically demonstrated a novel chiral metamaterial to achieve broadband asymmetric transmission(AT)of linearly polarized electromagnetic waves in terahertz(THz)band.The proposed metamaterial unit cell exhibits no rotational symmetry with vanadium dioxide(VO_(2)) inclusion embedded between Dirac semimetals(DSMs)pattern.The resonant frequency of AT can be dynamically tunable by varying the Fermi energy(EF)of the DSMs.The insulator-to-metal phase transition of VO_(2) enables the amplitude of the AT to be dynamically tailored.The transmission coefficient|T_(yx)|can be adjusted from 0.756 to nearly 0 by modifying the conductivity of VO_(2).Meanwhile,the AT parameter intensity of linearly polarized incidence can be actively controlled from 0.55 to almost 0,leading to a switch for AT.When VO_(2)is in its insulator state,the proposed device achieves broadband AT parameter greater than 0.5 from 1.21 THz to 1.80 THz with a bandwidth of 0.59 THz.When the incident wave propagates along the backward(-z)direction,the cross-polarized transmission|T_(yx)|reaches a peak value 0.756 at 1.32 THz,whereas the value of|T_(xy)|well below 0.157 in the concerned frequency.On the other hand,the co-polarized transmission|T_(xx)|and|T_(yy)|remained equal in the whole frequency range.This work provides a novel approach in developing broadband,tunable,as well as switchable AT electromagnetic devices.

二维透射式Terahertz波时域谱成像研究

通过THz(Terahertz)波的相位信息和振幅信息来解析出样品某些可用于成像的参量;并且对THz波相位信息成像和振幅信息成像进行了比较.结果显示当样品对THz波的吸收比较小时,利用THz波的相位信息进行成像比通过振幅信息进行成像质量要好一些;时域谱峰值位置的漂移会对相位信息成像产生较大的影响.实验中发现输出光谱中出现了劈裂现象,即由输入的单峰变成了双峰.分析表明,这一现象是由样品内部厚度或折射率突变导致的,该现象可用于THz波轮廓成像研究.

Propagation characteristics of oblique incidence terahertz wave through non-uniform plasma

The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.

Low-loss terahertz waveguide with InAs-graphene-SiC structure

We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient （αloss 0.55 dB/m） for fundamental mode （LP01） when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a fiat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.

Metamaterial Absorbers in Terahertz Band

In recent years, a great deal of effort has been made to a create terahertz （THz） wave absorber based on metamaterials （MM）. Metamaterials absorbers have a variety of potential applications including thermal emitters, detector, stealth technology, phase imaging, etc. In this paper, we firstly introduce the basic structure and work principle of the THz MM absorbers, and a transmission line model is developed for devices analysis. To expand the application of THz absorbers, dual-band and broadband THz MM absorbers are designed, fabricated, and measured. At the end of this article, the future development trends of MM absorbers are discussed.

Efficient and multifunctional terahertz polarization control device based on metamaterials

Terahertz polarization devices are an important part of terahertz optical systems.Traditional terahertz polarization devices rely on birefringent crystals,and their performances are limited by the material structures.In this work,we theoretically demonstrate that the metamaterial consisting of the medium and the periodic metal band embedded in the medium can control broadband polarization effectively.The transmission length of the subwavelength waveguide mode gives rise to a broadband transmission peak.The resonant cavity structure formed by the dielectric layer and the waveguide layer possesses a high transmission efficiency.By optimizing the metamaterial structure parameters,we design a high-efficient(>90%)quarter-wave plate over a frequency range of 0.90 THz-1.10 THz and a high-efficient(>90%)half-wave plate over a frequency range of 0.92 THz-1.02 THz.Besides,due to the anisotropy of the structure,the metamaterials with the same structural parameters can achieve the function of the polarized beam splitting with an efficiency of up to 99%over a frequency range of 0.10 THz-0.55 THz.Therefore,the designed metamaterial has a multifunctional polarization control effect,which has potential applications in the terahertz integrated polarization optical system.

基于太赫兹成像检测技术与特征提取方法结合巴旦木饱满度检测方法研究

巴旦木是一种营养丰富的坚果,对巴旦木的品质进行检测具有重要的经济价值和实际意义。由于巴旦木具有较为坚硬的外壳,传统的检测手段较难实现内部检测,因此,采用新兴的太赫兹透射成像检测技术,开展巴旦木饱满度的检测研究。首先采集不同饱满度巴旦木的太赫兹透射图像,并且从太赫兹图像的感兴趣区域分别提取无样品区域、空壳区域和满仁区域的太赫兹光谱信息;为了提高模型的精度,减少计算量,采用竞争性自适应重加权算法(CARS)、无信息变量消除(UVE)、连续投影算法(SPA)、蒙特卡罗无信息变量消除法(MCUVE)和遗传算法(GA)对太赫兹光谱信息进行特征提取,建立对应的最小二乘支持向量机(LS-SVM)、随机森林(RF)和K-近邻(KNN)定性判别模型,对巴旦木的饱满和空壳区域进行检测和鉴别。此外,对太赫兹特征图像转为JPG格式,接着转化为RGB格式进行G通道提取和图像二值化分离出外壳和果仁图像,检测饱满度为太赫兹特征图像的壳仁像素点之比;对原始图像进行轮廓提取和图像二值化分离出外壳和果仁图像,实际饱满度为原始图像的壳仁像素点之比。通过计算检测饱满度和实际饱满度的误差,证明了太赫兹透射成像技术检测巴旦木饱满度的可行性。建立的KS-GA-RF模型的鉴别效果最优,准确率为98.21%;通过壳仁像素点之比分别计算出对应的检测饱满度和实际饱满度,误差为16%。研究验证了采用太赫兹图、谱相融合的方法,可以很好地实现对巴旦木内部种仁饱满度可视化检测,为巴旦木的准确分级提供了新的思路,也为太赫兹成像技术检测其他坚果饱满度提供了理论参考,具有重要的应用价值。

频率可调谐的双偏振非对称传输器件

为了研究太赫兹超构材料的可调谐非对称传输特性,本文基于相变原理提出一种类S型的双层结构,采用有限积分算法求解其偏振传输特性。利用温度调控二氧化钒的相变特性,实现了频率可调谐的双偏振非对称传输效应。在宽角度入射范围内,45°线偏振光的非对称传输特性保持着较高的工作效率,倾斜入射角为60°时,效率优于0.4,且绝缘态和金属态下的谐振频率几乎保持不变,谐振频率的可调谐度为16.3%。本文所提出的频率可调谐双偏振非对称传输器件在偏振调控、太赫兹通信和太赫兹芯片领域具有潜在的应用前景。

应用于太赫兹波驱动的DNP-NMR传输线

太赫兹波驱动的动态核极化增强核磁共振波谱系统可大幅提高信号灵敏度和缩短检测时间。该系统需采用传输线在驱动源回旋管与谱仪之间进行太赫兹波传输。本文针对400 MHz增强核磁共振系统设计了由准光模式变换器和波纹波导组成的太赫兹传输线,并进行了相关实验测试,测试结果表明准光模式变换器可将263 GHz回旋管TE 03模式转换成准高斯波束,其高斯成份为97%,整个传输线最终输出波束的高斯成份为96.3%。

等离子体处理制备柔性低损耗ABS/Ag太赫兹空芯波导及其传输可靠性研究

等离子体处理ABS管提升了ABS/Ag镀层太赫兹空芯波导的性能。胶带法测试结果表明,等离子体处理后,银镀层的附着力由5级提升至2级。等离子体处理后的ABS管内表面银层的均匀性和致密度更高,高质量的银层有利于降低波导的损耗。未经等离子体处理的4.2 mm内径的ABS/Ag镀层空芯波导在0.3 THz和0.1 THz时的直线损耗分别为0.72 dB/m和1.47 dB/m,等离子体处理后其损耗分别降至0.70 dB/m和1.44 dB/m,且波导能够在冷热环境中稳定传输太赫兹波。等离子体处理后的样品在超过200小时的湿热老化和16次的高低温循环老化试验后直线损耗升高小于0.1 dB/m,而未经等离子体处理的样品的损耗升高大于1 dB/m。研究结果表明,等离子体处理后的ABS/Ag镀层太赫兹空芯波导损耗更低、传输可靠性更高、耐老化性更好,可用于构建下一代通信、传感及太赫兹成像系统等。

太赫兹辐射调控神经元突触传递的动力学特征提取方法

突触后电位是神经元传递信息的重要载体,该信号的动力学分析是神经科学研究中的常用方法。但目前传统的分析方法中多采用手工提取动力学特征值,分析数据量有限。针对此缺陷,本文提出了一种神经元突触传递的动力学特征提取方法。在该方法中,采用低通滤波器提取有效数据,降低了数据计算量和复杂性;采用中值滤波算法去除了信号中随机噪声、刺激伪迹,并校正基线漂移,利用曲线拟合提取了突触后电位信号波形斜率特征值,实现突触后电位信号变化趋势的可视化。该特征提取方法的平均绝对百分比误差一般在5%左右,幅度特征值的平均绝对百分比误差一般在3%左右。同时取95%的置信区间,降低波形的测量误差,使得有效数据正检率指标高达98%。结果表明该特征提取方法可提取信号中的有效数据,并能保证特征值提取的精度,减小了人工提取存在的误差。通过神经元响应数据,验证了该方法的可行性,提出了太赫兹调控神经元突触传递的猜想。

太赫兹科学与电子信息学报

太赫兹技术在下一代通信、生物成像、质量监测等领域应用潜力巨大,高品质太赫兹波导的研制使轻量化、小型化太赫兹系统成为可能,是推动太赫兹技术发展的关键。本文根据不同基材,将太赫兹波导分为金属波导、聚合物波导及复合波导,对其发展情况进行梳理,并对太赫兹聚合物波导这种高柔性、低成本导波技术进行重点介绍,讨论其不同的导光机制;最后对太赫兹导波技术进行了总结,并针对制约太赫兹波导商品化推广应用的瓶颈问题进行了初步探讨。

一种基于Dirac半金属的可调控极化偏转器件的仿真分析

本文提出了一种基于体Dirac半金属(Bulk Dirac Semimetal,BDS)的动态超材料结构极化偏转器.与传统的极化偏转器不同,该偏转器可以通过改变费米能级来动态控制偏振转换率和不对称传输.模拟结果表明,当BDS的费米能级调整为90 meV时,偏转器的偏振转换率在1.085~1.872 THz频率范围内都保持在90%以上(带宽为0.787 THz),在1.159 THz处偏振转换率达到峰值98%.该偏振转换器的不对称传输参数在1.229~1.831 THz大带宽范围内大于60%.本文还研究了偏振旋转角、椭圆度角、表面电流和电场分布情况以阐明该器件的极化转换特性和物理机制;通过施加栅极电压控制BDS费米能级,实现了对该极化偏转器的偏振转换率以及不对称传输的动态调谐.该极化偏转器的可调谐不对称传输特性,为基于动态不对称传输所设计的多路复用器、太赫兹二极管等设备的制造提供了新的思路.

太赫兹大气传输特性的研究概况与应用展望

介绍了太赫兹技术的发展概况及其在部分应用场景中的优势,如在雷达中具有高分辨率、强反隐身特性等。在太赫兹大气传输特性方面,重点介绍了MPM模型基本原理,并对主流的大气传输模型如ATM模型、AM模型做了简要的介绍与比较。同时介绍了近年来国内外对太赫兹大气传输特性的研究概况与新的进展,并对太赫兹技术的发展进行了总结与应用层面的展望。

左/右圆极化波操控的多功能太赫兹超表面

太赫兹波是指频率位于0.1~10 THz之间的电磁波,介于微波和红外之间,具有穿透力强、分辨率高、无电离辐射等优势,在安全检测、医学诊断、材料分析等领域有广泛应用前景。太赫兹技术发展与应用对太赫兹波多功能调控器件的需求日益增长,传统介质在太赫兹波段响应微弱,超表面因其能够在波长尺度对太赫兹波进行调控,而且在加工和设计方面具有低成本、小体积等优势,受到研究人员广泛关注。目前已报道超表面太赫兹功能器件,或多或少存在着功能单一,而且受单一偏振波限制。当前,研究人员提出方案主要是改变亚波长超表面结构的几何形态和排列方式引入传输相位或通过旋转单元结构引入几何相位实现对电磁波参数调控,但是单种调控方式仍然存在可调谐性差等问题,因此设计基于传输相位和几何相位理论协同调控的超表面电场调控器件显得更具前瞻性和意义。引入一种全新对角双十字结构超表面,该超表面单元结构由顶层金属图案、中间介质层和底层金属板组成,结合传输相位与几何相位协同作用,完成对左圆偏振波和右圆偏振波独立调控。在频率为1.1 THz的左/右圆偏振波入射时,该超表面展现出多种功能,包括不同拓扑荷数的涡旋波束、波束分束、涡旋波分束、聚焦波束等。这种创新结构设计为多功能、多偏振的太赫兹调控器件研究提供了崭新的思路,为太赫兹无线通信领域的应用场景提供了潜在的可能性,同时也为太赫兹技术的不断发展提供了强大的推动力。在未来的研究中,可以通过改变超表面尺寸将其进一步拓展到微波和光学领域。

手性THz超表面传感器对乳酸对映体的灵敏检测

基于柔性扭曲双层手性超表面传感器,采用太赫兹时域光谱技术,以手性乳酸(LA)对映体为研究对象,提出一种在太赫兹波段实现手性物质浓度传感和对映体识别的方法。结果表明,手性超表面传感器的圆二色谱(TCD)会随着浓度的增加而发生偏移,且不同的手性对映体偏移量不同,左旋性LA(L-LA)和右旋性LA(D-LA)的最高检测灵敏度分别为2.6 GHz/(mg/mL)和1.9 GHz/(mg/mL),检测限低至0.01 mg/mL。手性超表面传感器在LA传感和手性识别方面的巨大潜力,为手性对映体的灵敏检测提供了一种高效、低成本的技术方法。