基于四波混频效应的窄带太赫兹波源

采用频率差在太赫兹范围的双波长激光器进行泵浦,利用光纤的四波混频效应,得到结构紧凑、频率可调的窄带太赫兹波源。为减小光纤材料对太赫兹波的吸收,采用了表面发射机制。从耦合波理论出发,详细分析了保偏光纤中的四波混频过程,得到了太赫兹波输出功率的解析表达式,并讨论了实现相位匹配的条件。结果表明,太赫兹波功率与泵浦光功率和光纤长度成正比,与太赫兹波长的3次方成反比。当泵浦光峰值功率为1 kW,在6 THz处得到的太赫兹波峰值功率达350 mW,功率转换效率约为0.01%。通过合理设置泵浦波长,可以实现太赫兹辐射在3~8 THz范围内连续调谐。该方案提供了一种新型的高功率、紧凑型的窄带太赫兹辐射源。     

基于双尺度4分离层优化的石墨烯太赫兹宽带吸波结构

为实现对未来远程太赫兹雷达的高效对抗与隐身,针对典型太赫兹雷达工作频率设计了一种石墨烯太赫兹宽带吸波结构。宽带吸波结构以表层金属层/石墨烯层/介质层/底层金属层为基本吸波结构单元,利用遗传算法对双尺度基本吸波结构单元进行4分离层优化设计,确定宽带吸波结构的各层结构参数。仿真结果表明:宽带吸波结构在0.138 THz～2 THz频率范围内吸收效率优于80%,在0.157 THz～2 THz频率范围内吸收效率优于97.46%,典型太赫兹雷达工作频率处吸收效率均优于92.27%,满足太赫兹雷达对抗与隐身要求。     

新型有机晶体及超宽带太赫兹辐射源研究进展

非线性光学晶体是非线性光学频率变换技术中的核心器件。近些年,为进一步提高基于非线性光学频率变换技术产生太赫兹波的输出能量、转换效率,拓宽产生太赫兹波的带宽,多种新型有机晶体得以发展,并凭借其更加出色的非线性光学性质,成为产生太赫兹波的理想材料。本文按照晶体类型介绍了目前可产生THz波的多种有机晶体的性质,并总结了基于多种有机晶体的超宽带太赫兹辐射源的国内外研究进展,同时结合THz光谱检测技术的应用需求分析了基于有机晶体宽带THz辐射源的发展趋势以及所面临的关键科学问题。     

太赫兹mesh带通滤波器的设计与仿真

基于太赫兹波的大气吸收窗口,设计了一款四级级联的太赫兹mesh带通滤波器。此滤波器的中心频率为0.25 THz,在3 dB处带宽为0.1 THz,在通带内的插入损耗为1.5 dB,纹波系数小于0.5 dB,在室温下通带内的透过率能达80%以上,且此滤波器的中心工作频率和带宽可以通过缩放mesh槽孔的尺寸来调节。利用电磁仿真软件HFSS,结合周期边界条件及理想匹配层吸收边界条件模拟了太赫兹mesh带通滤波器的mesh排列方式、介质衬底及不同入射角度的入射波、不同极化方式等因素对滤波器透过率、插入损耗的影响。     

碳纳米管薄膜周期结构的太赫兹表面等离子波特性研究

在获得太赫兹波段碳纳米管薄膜的介电特性基础上,利用数值THz时域光谱技术研究了碳纳米管薄膜栅周期结构的表面等离子激元的传播特性和局域化现象. 研究结果表明,在栅周期为168 μm时,频率在0.5-2.5 THz之间出现两个等离子模式的共振峰值,分别位于0.99 THz和1.95 THz,这与理论计算结果相符合. 数值计算的表面等离子激元传播距离与理论预测值相一致,达到了146 μm. 此外,分析了栅厚度与栅宽度变化对表面等离子波特性的影响. 关键词： 太赫兹 碳纳米管 表面等离子波     

一种新型的可调太赫兹辐射源

美国科学家发明了一种新的可调太赫兹（THz，1THz=10^12Hz）辐射源，其功率是以前的太赫兹辐射源10，000倍．与大多数其他产生太赫兹辐射的系统不同，该新的可调辐射源采用商用集成电路中所使用的CMOS（互补金属氧化物半导体）技术．研究人员希望他们的新技术可以使太赫兹辐射得到更广泛的应用．     

一种宽带瓦量级交错双栅脊波导返波振荡器的研究

为满足太赫兹领域对大功率、宽带宽的太赫兹辐射源的需求,提出了一种新型交错双栅脊波导（RDSG）慢波结构。设计并优化了交错双栅脊波导返波振荡器的高频结构,同时对交错双栅脊波导和常规交错双栅的高频特性进行了仿真和对比,结果表明：当二者相速度接近时,交错双栅脊波导拥有更宽的“冷”通带带宽和更高的耦合阻抗。PIC仿真结果表明,在1 THz频段,交错双栅脊波导返波振荡器拥有超过175 GHz的可调谐带宽以及1.1 W的输出功率,比相同工作条件下的常规交错双栅结构输出功率了提高34%～42%。     

太赫兹随机激光研究

本刊讯太赫兹（Terahertz,THz）波通常指的是频率在0．1～10THz范围内的电磁辐射,其独特性能给通信、雷达、电子对抗等诸多领域带来了深远的影响。而太赫兹辐射源是太赫兹技术是否转化为现实生产力的关键环节,然而目前仍然缺乏低造价、高功率、和便携式的低温太赫兹光源,从而限制了太赫兹在实际中的应用。因此寻找新的太赫兹源成为当代太赫兹研究领域的主要目标之一。     

0.8 THz再生反馈振荡器的仿真模拟研究

随着太赫兹技术的发展,高频率、大功率的太赫兹辐射源一直是国内外研究的热点。再生反馈振荡器作为一种新型太赫兹源器件,具有可行性高、功率大的优点。基于0.8 THz太赫兹波成像系统的需求,采用折叠波导慢波结构,对再生反馈振荡器进行设计与研究。首先对0.8 THz折叠波导慢波结构进行设计并使用CST微波工作室中的本征模求解器进行参数优化,再通过CST粒子工作室中的PIC仿真模块对整管进行热特性仿真,验证了方案的可行性,仿真结果显示,最终可产生60 mW的稳定输出信号。     

基于三层光栅结构的超宽带太赫兹吸收体

基于等效介质膜理论及多层减反膜原理设计了用于超宽带太赫兹吸收体的三层微结构光栅,光栅基质采用重掺硼硅材料.用有限时域差分法分析了光栅周期、光栅宽度和深度对太赫兹吸收体反射系数的影响.数值分析结果表明,在低于3THz波段,吸收率高于98%的带宽为1.3THz,吸收率高于95%的带宽达2.1THz.用严格耦合波理论对该三层光栅的高吸收现象进行理论分析,分析结果表明,光栅多级衍射的相互作用减少了入射面的反射率,增大了该吸收体的吸收率.进一步优化三层光栅微结构的参量,在0.6~6THz范围内实现了大于95%的太赫兹吸收.基于光栅结构的吸收体结构简单,易于设计与分析,可以应用于太赫兹成像与探测应用领域.     

SIMULATION OF CARBON NANOTUBE THz ANTENNA ARRAYS

A novel THz antenna structure, made of carbon nanotube arrays is suggested. Using CST MICROWAVE STUDIO (CST MWS), the capabilities of carbon nanotube terahertz (THz) antenna arrays have been simulated. The dependence of gain, upon geometrical factors, e.g., nanotube diameter, nanotube length and the inter-tubes distance, is shown. The directivity patterns of antenna arrays and the surface current distribution of an antenna have been shown by simulation. These results could be used in the design of carbon nanotube THz antenna arrays.     

Properties of terahertz wave generated by the metallic carbon nanotube antenna

The properties of terahertz (THz) radiation pulses emitted by a metallic, large aspect ratio carbon nanotube antenna have been studied both in the THz waveforms and field distribution. The peak THz field up to 2.66 and 1.26 kV/cm are observed at the probe points. The proposed antenna is designed to operate for dual frequency applications from 2.36 to 2.58 THz and from 7.27 to 7.5 THz for less than -10 dB return loss.     

Radiation Properties of Carbon Nanotubes Antenna at Terahertz/Infrared Range

The geometric structure and the terahertz/infrared radiation characteristics of carbon nanotubes dipole antenna arrays have been investigated by CST MICROWAVE STUDIO based on finite integral methods. In terahertz and infrared frequency span, the antenna properties such as electrical field distributions, scattering parameters, standing wave ratio, gain, and two dimension directivity patterns are discussed. Our results show that N × N antenna arrays have higher radiation efficiency than single carbon nanotube dipole antenna. This work was supported by National Natural Science Foundation of China (60571026, 10396160).     

基于可调谐准高斯波束太赫兹源的成像系统研究

报道了一种基于频率可调谐准高斯太赫兹波束的透射成像系统.研究表明,在这种成像系统中太赫兹波束具有良好的空间分布特性,其波束质量因子M²_x＝1.15,M²_z＝1.25,波束传输特性和聚焦特性良好.实验结果反映出成像系统的空间分辨能力与典型太赫兹波长(250μm)相接近.在太赫兹波输出1.0—2.5THz范围内,成像系统信噪比大于1000dB;在1.8THz处,信噪比 关键词： 太赫兹波 太赫兹成像 太赫兹探测     

Analysis of graphene based optically transparent patch antenna for terahertz communications

With and without multi walled carbon nanotube (MWCNT) loaded graphene based optically transparent patch antennas are designed to resonate at 6 THz. Their radiation characteristics are analyzed in 5.66–6.43 THz band. The optically transparent graphene is deployed as the patch and ground plane of the antennas, which are separated by a 2.5 μm thick flexible polyimide substrate. By shorting the microstrip line and ground plane of the antenna with a MWCNT via, the return loss of the antenna is improved. The peak gain of 3.3dB at 6.2 THz and a gain greater than 3dB in 5.66–6.43 THz band is obtained for antenna loaded without MWCNT. Both the antennas achieved a −10dB impedance bandwidth of 12.83%. Gain, directivity and radiation efficiency of the proposed antennas are compared with conventional transparent patch antennas and graphene based non-transparent antennas. The antenna structures are simulated by using finite element method based electromagnetic simulator-Ansys HFSS.     

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.     

Terahertz wave narrow bandpass filter based on photonic crystal

We designed a narrow bandpass terahertz wave filter using photonic crystals with a line defect. An inserted linear defect in one-dimensional photonic crystal structures for a channeled filtering in the terahertz range are studied and designed theoretically. By using transfer matrix method, we examined the transmittance spectra for the proposed terahertz wave filter has a 3 dB transmission loss bandwidth of 20 MHz ranging from 0.29998 THz to 0.30001 THz. The simulated results show that a very narrow transmission band and high transmission (higher than 99.99%) centered at λ₀, and very sharp edges can be achieved.     

超低温高电场下GaAs的电子太赫兹功耗谱的研究

利用自由空间太赫兹电光取样方法,测量了在高电场下,GaAs中受飞秒激光脉冲激发的电子所辐射出的太赫兹电磁波,发现从样品中辐射出的和电子加速度成正比的太赫兹电磁波电场强度E_THz（t）,表现出双极特性.通过分析GaAs中辐射出的太赫兹电磁波的傅里叶变换谱,首次实验上得到在阶跃电场下的GaAs的电子太赫兹功耗谱.研究发现,当电场小于50 kV/cm时,由电子谷间散射引起的负功耗（即增益）的截止频率ν_c,随着电场的增大而增大;当电场大于50 kV/cm时,负功耗的截止频率ν_c开始在750 GHz（10 K）附近饱和. 关键词： 太赫兹 非平衡载流子 功耗谱 谷间散射     

A TERAHERTZ PHASE FREQUENCY CHANGER WITH THE CRYSTAL QUARTZ PHASE SECTIONS

A phase frequency changer (PFC) for quasi-optical transmission line with phase sections made of crystal quartz and polarizers executed on the basis of small-period wire gratings has been considered. The PFC is intended for operation in terahertz (THz) frequency region. It has been examined at the frequency f _o= 0.89THz. The influence of the differential phase shift deviation in the sections on the output signal spectrum and the influence of the sections mismatch on the reflection signal spectrum have been considered. In the frequency region ± 10% f _o the levels of the spurious spectral components of output signal are less than −40 dB with regard to the level of the useful signal of the shifted frequency. The levels of all spectral components of the reflection signal are less than −60 dB with regard to the level of the useful component of the PFC output signal.     

Characterization of the radiation from single-walled zig-zag carbon nanotubes at terahertz range

This paper investigates the radiation characteristics of metal single-walled zig-zag carbon nanotubes as a dipole antenna at terahertz wave range. The current distribution, input impedance and mutual impedance are calculated for various geometrical parameters of vertically-aligned carbon nanotubes. The numerical results demonstrate the properties of the antenna depending strongly on the geometrical parameters such as the radius, the lengths of carbon nantobues, and the spacing between nanotubes. It is found that the zig-zag carbon nanotubes exhibit very high input impedance and the mutual impedances for antenna array applications. These unique high impedance properties are different from the conventional metal thin wire antenna. The far-field patterns and gain of antenna array are also calculated. The maximum gain of array of 100-element array is up to 20.0~dB, which is larger than the gain of 0.598~dB of single dipole antenna at distance d = 0.5\lambda .