亚波长线栅太赫兹偏振分束器的研究

为了提高工作在太赫兹波段偏振分束器的性能,采用激光诱导与化学镀铜的方法在聚酰亚胺衬底上制作了亚波长周期金属线栅太赫兹偏振分束器,并以返波振荡器作为太赫兹辐射源搭建了偏振分束特性测试系统。当入射波频率为340GHz、入射角为45°时,测得在入射波偏振在0°～180°变化过程中,该偏振分束器具有良好的偏振分束特性,透射和反射的消光比分别为27.3dB和10.5dB,插入损耗分别为0.13dB和0.32dB;用太赫兹时域光谱系统测得偏振分束器在0.2THz～1.5THz频域内透射消光比大于18dB。结果表明,测试结果与时域有限元方法模拟结果基本吻合。     

太赫兹光子晶体光纤与天线设计

以聚甲基丙烯酸甲酯(PMMA)材料为基质,设计了一种空芯多孔包层结构的太赫兹光纤,中心的大孔缺陷用于传输太赫兹波,周围四层小孔可以将太赫兹波的传播限制在缺陷内部。利用COMSOL软件对光纤的损耗特性进行仿真分析发现,光纤在0.6 THz的泄露损耗低于0.1 dB/m,具有良好的传输特性。和金属波导口可以当作天线辐射电磁波的原理相似,光纤的端面也可以作为天线将内部传输的太赫兹波向外辐射,通过仿真分析,天线在0.59~0.61 THz的回波损耗低于-25 dB,方向性系数大于20 dB,半功率波束宽度约为13。     

Terahertz polarization beam splitter based on photonic crystal and multimode interference

We design a compact terahertz （THz） polarization beam splitter. Both plane wave expansion method and fi- nite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The designed polarization beam splitter can split TE-polarized and TM-polarized THz waves into different propagation di- rections. The simulation results show that the extinction ratios are larger than 18.36 dB for TE polarization and 13.35 dB for TM polarization in the frequency range from 1.86 THz to 1.91 THz, respectively. The designed polarization beam splitter has the advantages of small size and compact structure with a total size of 4.825 mm×0.400 mm.     

基于波导缝隙阵列的新型太赫兹频率扫描天线

为缩短太赫兹系统成像时间,该文提出将频率扫描天线应用于太赫兹成像系统中,并设计了一种基于波导缝隙阵列的太赫兹频率扫描天线。该文采用泰勒综合法降低副瓣电平,通过软件仿真结合功率传输法设计最优的缝隙分布。太赫兹波导缝隙阵列天线具有加工简单、成本低的优势,通过太赫兹准光测试系统对天线性能进行测试,实测天线扫描角度可达40°,增益约为15 dB,副瓣电平抑制优于–20 dB。测试结果表明太赫兹波导缝隙天线具有扫描角度大和副瓣低的优良特性,在太赫兹成像和目标探测等领域有巨大的应用价值。      

Polarization-Insensitive Operation of Lithium Niobate Mach–Zehnder Interferometer With Silica PLC-Based Polarization Diversity Circuit

We demonstrate the polarization-insensitive operation of a Mach-Zehnder interferometer (MZI)-based lithium niobate switch with a silica waveguide polarization beam splitter. The splitter is composed of an MZI with a half wave plate installed in one arm, and exhibits a polarization extinction ratio of more than 15 dB. The switch functions for both polarizations with an extinction ratio of more than 20 dB, a polarization-dependent loss of 0.1 dB and a switching speed of 40 ps.     

太赫兹波段复合型FSS带通滤波器的分析与设计

利用谱域法对频率选择表面 (frequency selective surface,FSS) 结构进行理论分析,设计了中心频率为0.338 THz工作在大气通信窗口的复合型FSS带通滤波器。该滤波器是对圆环槽单元滤波器进行改进,增加了三极子单元,通过研究结构参数对滤波性能的影响关系,进行结构优化。实验表明,该滤波器综合滤波性能更好,3 dB带宽可以达到69.5 GHz,回波损耗小于-13.46 dB,带内插入损耗小于0.45 dB,带内纹波低到0.1 dB,且通带平坦,有较好的带外抑制和矩形系数,边带比较陡峭。同时该滤波器在不同极化波和相同极化波不同入射角度入射时都有很好的频率稳定性,能有效地用于太赫兹通信。     

Design and Analysis of an Ultra-Compact and Ultra-Wideband Polarization Beam Splitter Based on Coupled Plasmonic Waveguide Arrays

We present the design of an ultra-compact polarization beam splitter where three symmetrical dielectric channel waveguides are hybrid integrated with Au plasmonic waveguide arrays. Ultra-wideband operation over 50 THz with the insertion loss less than 2 dB for both transverse electric and transverse magnetic mode are predicted. The extinction ratio is better than 15 dB for both polarizations and it is realizable on a chip size as small as 0.93times4.2 mum².     

Ultra-compact 1 × 8 Channel terahertz Wave Power Splitter

Relying on 1?×?2 photonic crystal waveguide and photonic crystal resonator, a compact eight-channel terahertz wave power splitter is proposed. The mechanism of such a device is further theoretically analyzed and numerically investigated with the aid of the plane wave expansion method and the finite-difference time-domain method. With an appropriate design, the proposed power splitter can split the input terahertz wave energy equally into eight output ports at the frequency of 0.667 THz. Furthermore, the total size of the present device is of 4.33 mm?×?3.74 mm. Due to its small size, the multi-channel terahertz wave power splitter has practical applications in the terahertz wave integrated circuit fields.     

0.14 THz双注折叠波导行波管的高频系统设计

随着太赫兹通信技术的发展,对于0.14 THz折叠波导行波管(FWTWT)的研究需求向着更高的功率和更宽的带宽发展。对双注行波管中的双路折叠波导慢波电路进行分析,得到不同参数下的高频特性变化规律。并对双路折叠波导慢波电路的功率分配和功率合成效率进行分析计算,得到功率合成效率96.3%。最后对双路慢波电路、功率分配/合成器和集中衰减器进行建模,并对注波互作用进行计算。在高压15 kV和单注电子的发射电流为40 mA条件下,得到0.14 THz频率下的合成输出功率为56 W,增益为31.4 dB,3 dB带宽为7 GHz。     

垂直双空芯宽带太赫兹偏振分离器

针对太赫兹波的特点,利用折射率匹配耦合原理,设计了一种垂直双空芯结构的偏振分离器件。与传统的分离器件相比,它具有以下优点:（1）双芯折射率匹配度高,使得对应的偏振模式所需要的分离长度很短;（2）采用双空气纤芯结构,降低材料对太赫兹波的吸收损耗;（3）通过设计,令其发生耦合的两个纤芯相互垂直,从而使y偏振模的折射率曲线部分重合,大大扩展了工作带宽的范围,其工作带宽达到了0.17 THz。此外,由于器件结构简单对称,降低了光纤的设计和制备难度,使其在太赫兹网络中具有很高的应用价值。     

宽带调谐光子晶体光纤多功能太赫兹器件

基于液晶分子的指向矢随外加电场改变而变化的特点,设计了一种新型电场调制液晶太赫兹器件。利用全矢量平面波展开法和光束传播法分别研究了光子晶体光纤的带隙位置和传输光谱的电场分布。同时,利用时域有限差分法计算了液晶分子指向矢随外电场的变化关系。结果显示该器件不仅可以在0.55 THz的宽带范围内实现开关功能,且具有耦合损耗低、消光比高等优点,消光比为30.78 dB。当太赫兹波的入射频率满足光纤的单偏振条件时,该器件还具有偏振控制功能,能够改变传输模式的偏振状态。     

太赫兹矩形波导与共面波导耦合结构设计

太赫兹（THz）波位于微波与红外光波之间,现有微波和光波段波导技术应用正在向THz波段拓展。但是,由于水汽对THz波的强吸收及制造工艺等原因,THz器件主要是平面结构,而THz源及其传输需要用矩形波导。因此,矩形波导与共面波导之间的转换结构成为决定元件和系统性能的关键部分。该设计利用脊波导进行阻抗匹配及电磁场模式转换,实现THz波矩形波导到共面波导的高效率耦合。结果表明,在0.2~0.4 THz频段内,该转换结构的传输系数(S₂₁)高于?3 dB,可以对THz电磁场进行高效率转换。该结果可用于太赫兹分子探测、太赫兹通信等领域,为0.2 THz以上太赫兹的模式转换提供了一种可行方案。     

基于二氧化硅薄膜夹层式亚波长金属光栅的宽波段太赫兹偏振分束器

设计出一种结构新颖的宽波段太赫兹偏振分束器,这种偏振分束器由夹层式亚波长金属光栅制成。亚波长金属光栅偏振分束器可以将入射的任意自然光分成两束偏振状态垂直的线偏振光。其中,TE模反射而TM模透射。设计的偏振分束器在3.5~5.5 THz波段可以达到很高的衍射效率与消光比。但是,在光栅的实际制作过程中,加工技术的缺陷引起的误差大大影响了光栅的性能,比如衍射效率,消光比等。因此文中对一些结构参数进行了计算,从计算结果可以看出这种偏振分束器也有很好的工艺容差。当覆盖层厚度D1与底层介质厚度D3的变化范围分别为1~1.2 m和2.8~3 m时,T0TM大于96.9%,R0TE大于98.7%。Tc和Rc分别大于31 dB和33.4 dB。结果显示,设计的偏振分束器在2 THz的带宽10的大角度范围内,衍射效率高于90%,消光比大于20 dB。因此文中设计对于太赫兹调制器件的研究,以及太赫兹通信系统的集成都有很大的参考价值。     

0.41 THz折叠波导慢波结构分析与设计

在0.14 THz,0.22 THz和0.34 THz折叠波导行波管研制的基础上,讨论了0.41 THz折叠波导行波管慢波结构设计与加工的可行性,分析研究了折叠波导慢波结构弯曲处直角弯曲与半圈弯曲、方形电子注通道与圆形电子注通道对色散特性、耦合阻抗、带宽、冷损耗和增益的影响。考虑了慢波结构中增加理想衰减器对该行波管带宽和增益的影响,得到了0.41 THz折叠波导行波管慢波结构的初步设计方案,为太赫兹折叠波导行波管的继续发展打下了一定基础。     

Compact Bends for Achieving Higher Integration Densities for LiNbO$_{3}$ Waveguides

A new waveguide platform is demonstrated that allows the bend radii to be substantially decreased for titanium-diffused lithium-niobate (LiNbO₃) waveguides using vertically integrated arsenic-trisulfide (As₂S₃) overlay waveguides. Power is transferred from a Ti-diffused waveguide into the overlay waveguide using tapers, guided by the As₂S₃ waveguide through the S-bend region and transferred back into another Ti-diffused waveguide. This structure also behaves like a polarization beam splitter. We present simulation results as well as measurements to show the feasibility of achieving low loss and reduced bend radii for electrooptic waveguides.     

0.22 THz Waveguide Bandpass Filter with High Stop-Band Suppression

A terahertz (THz) waveguide band-pass filter using an iris inductive window coupled structure was designed and fabricated. The filter was designed at 0.22 THz with a pass band of 20 GHz. The measured results show that the center frequency is 0.218 THz with a pass band of 0.205 THz to 0.231 THz, the minimum insertion loss is 1.26 dB at 0.224 THz, and the return loss is less than 13.1 dB. The stop-band suppression is 65.6 dB at 0.193 THz and 51.8 dB at 0.243 THz, respectively, which means a good performance of high stop-band suppression. A good agreement exists between the measured S-parameters and the simulated ones, especially in the upper band. The proposed THz waveguide filter has potential applications in THz communications.     

双波长波片导致的脉冲分离对双色场辐射太赫兹波的影响

由于群速度的偏振依赖性,飞秒激光脉冲入射到双波长波片时出射光脉冲会分离为两个具有一定时间延迟的飞秒激光脉冲。从实验和理论模拟两方面研究了双波长波片导致的脉冲分离现象对飞秒激光双色场成丝辐射太赫兹(THz)波效率的影响。实验结果表明,脉冲分离导致的时间延迟会降低双色场辐射THz波的效率,可通过零级双波长波片缩短分离脉冲之间的时间延迟,有效提高THz波的产生效率。     

曲折双脊槽波导高功率宽频带太赫兹行波管

提出一种改进的曲折槽波导—曲折双脊槽波导提高太赫兹行波管的功率和带宽.针对这种新型慢波结构设计了一种新的传输波导作为输入输出能量耦合器.从高频特性仿真结果可以发现曲折双脊槽波导可以提高耦合阻抗并扩展带宽.此外, 粒子仿真结果表明当电子注加载27.4kV电压和0.25A电流时, 新型曲折双脊槽波导行波管在中心频率340GHz处输出功率能达到65.8W同时对应增益27.21dB.因此, 曲折双脊槽波导行波管可以用作宽带和高功率太赫兹辐射源.     

0.3 THz紧凑型反射面天线

介绍了一部工作在0.3 THz的紧凑型高增益反射面天线。该天线包括馈源喇叭、分光片以及反射面三个部分,天线的组成部件集成在一块底板之上,底板尺寸为19.4 cm×16.8 cm。首先,通过理论设计确定天线各个组成部分参数和布局;进而,通过精密机加工手段得到一体化的天线样机;最终,利用平面近场测试系统完成方向图测试。测试结果表明,天线增益大于40 dB,副瓣低于-10 dB,从而在紧凑空间内实现太赫兹高增益天线。     

Linear theory of slow wave cyclotron interaction in double-ridgedfolded rectangular waveguide

A general dispersion relation for slow wave cyclotron traveling wave interaction in a folded waveguide is derived from a fluid dynamical treatment. The serpentine structure is formed by folding a double-ridged rectangular waveguide so that the orientation of the magnetic field changes (H-plane bend) instead of the conventional E-plane bend configuration. The H-plane bend structure has the potential for the production of high power, broad band radiation. For a cold beam, the linear theory predicts a gain of 2.0-2.5 dB/cm and a bandwidth of 20-25% in the millimeter wave frequencies. The bandwidth is sensitive to the axial velocity spread of the beam. The bandwidth decreases to 10% at δυ_z/υ_z=3%. Means to suppress the backward wave oscillations have to be applied for using the full bandwidth