Investigation of Terahertz Wave Propagation Along Shielded Dielectric Multiple-Slot Waveguide

In this paper, a shielded dielectric multiple-slot waveguide is presented and demonstrated by theoretical calculation at terahertz frequencies. Some electromagnetic analysis of waveguide currently employed simplified intrinsic frequency dispersion models for the bulk conductivity of normal metals used in terahertz wave structures. This paper has compared various conductivity models for gold between 0.1-3 THz. The dielectric loss, conductor loss, total propagation loss with different conductivity models and E-field distribution has been obtained by numerically solving the complex eigenvalue equation for the propagation constant. The analysis results are in agreement with the assumption of R. Sun et al. and the experimental results obtained by H. Sun et al. The propagation loss deviation between various models is less than 3% at 0.2-0.5 THz. Comparisons with other slot waveguides are also given. The analysis results show that the proposed line has lower propagation attenuation than other slot waveguides.     

介质金属膜波导在G波段和4.3THz的传输特性

制作了具有不同介质膜厚度的大口径柔性介质金属膜波导,测试了金属膜波导和介质金属膜波导在G波段、4. 3 THz和中远红外等频段的传输特性.结果表明,波导的传输损耗在G波段随介质膜厚的增加而增加,孔径2. 6mm的金属膜波导在160 GHz传输损耗为2. 1 d B/m且在G波段波导的传输损耗对弯曲不敏感.在4. 3 THZ频点波导的传输损耗随介质膜厚的增加而减小,镀制介质膜可以大幅减小波导的传输损耗以及弯曲附加损耗,孔径3. 6mm介质膜厚为1. 2μm的介质金属膜波导的传输损耗为2. 84 d B/m.光斑能量则随介质膜厚的增加更加集中于低阶传输模式.     

Analysis of optically controlled planar dielectric waveguidesoperating in the millimeter-wave band using FDTD

The finite-difference time-domain (FDTD) technique is applied to the analysis of planar dielectric waveguides controlled by means of an optical beam. This beam, with an appropriate energy, induces a nonuniform plasma in a semiconductor layer deposited on the waveguide core. The resulting effects are analyzed through the phase dispersion characteristics. Due to the complexity of the problem, the FDTD formulation does not allow the calculation of the attenuation characteristic, particularly when the plasma presents an intermediate density, which causes a strong interaction with the guided mode. The simulations shown here suggest that the light beam may have an effective control of the phase response of a single waveguide and of the coupling between two parallel coupled waveguides     

Dielectric waveguides for millimetre-wavelength transmission

The letter describes the salient features of a parametric study of dielectric waveguides intended for millimetre-wavelength microwave transmission. The waveguide is an analogue of the monomode optical waveguide, and, if core and cladding are made from foam materials, with loss tangents of order 10?5, the HE11 mode attenuation is about 40 dB/km, and the group delay change is 0.35 ns/km over 1 GHz bandwidth centred at 40 GHz.     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

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。     

Investigation on propagation properties of terahertz waveguide hollow plastic fiber

The propagation properties of terahertz (THz) waveguide plastic hollow fiber have been investigated in this paper. The effects of radiation frequency, bore diameters and dielectric coating layers on the waveguide property have been shown and discussed. The results show that the attenuation loss of TM mode increases and that of TE mode decreases as radiation frequency increases. The attenuation loss decreases with the increasing of fiber bore diameter. The attenuation loss decreases as the refractive index of dielectric coating layer and the ratio of the refractive index of outer dielectric layer to that of inner dielectric layer increase.     

A thin-film waveguide photodetector using hydrogenated amorphoussilicon

Metal-silicon-metal cladding layers on dielectric waveguides exhibit coupling and absorption characteristics that make them useful as photodetectors for integrated optical applications. Multilayer computer-modeling techniques were applied to waveguide photodetectors in order to investigate field and power distributions, as well as the attenuation and phase response in the guiding region. A waveguide photodetector based on amorphous silicon was fabricated and demonstrated     

Terahertz 2-D Photonic Crystal Waveguides

A 2-D photonic crystal waveguide with strong passbands in the THz frequency range is demonstrated. The 2-D metallic photonic crystal waveguide structure is bounded by parallel metal plates in the vertical direction and by a square lattice of metallized cylinders on the horizontal axis. The attenuation of the photonic crystal waveguide is experimentally determined and compared to the fundamental mode of a comparably sized rectangular waveguide. The measured dispersion characteristics of the waveguide are discussed, and the output is compared to a finite-difference time-domain simulation.     

FDTD microcavity simulations: design and experimental realizationof waveguide-coupled single-mode ring and whispering-gallery-mode diskresonators

We investigate the properties of high-Q, wide free-spectral-range semiconductor microcavity ring and disk resonators coupled to submicron-width waveguides. Key optical design parameters are characterized using finite-difference time-domain (FDTD) solutions of the full-wave Maxwell's equations. We report coupling efficiencies and resonant frequencies that include the effects of waveguide dispersion and bending and scattering losses. For diameters of 5 μm, the microcavity resonators can have Q's in the several thousands and a free spectral range of 6 THz (50 nm) in the 1.55 μm, wavelength range. Studies of the transmittance characteristics illustrate the transition from single-mode resonances to whispering-gallery-mode resonances as the waveguide width of the microring is increased to form a solid microdisk. We present nanofabrication results and experimentally measured transmission resonances of AlGaAs/GaAs microcavity resonators designed in part with this method     

太赫兹波在金属镀层空芯圆波导中的传输特性

文章理论分析了太赫兹波在金属镀层空芯圆波导中的传输特性.比较了在内直径为2mm的空芯圆波导中分别镀金、铅、镍不同金属时不同入射频率的太赫兹波的理论衰减常数,计算了镀不同金属而入射波波长一定的情况下波导中主模即最低模TE11模的衰减常数随波导内直径的变化情况.进一步研究表明Au,Ag,Cu均可作为空芯圆波导中优良的金属镀层以用于太赫兹波的低损耗传输.     

THz QCL波导结构研究与光束质量分析

THz量子级联激光器是理想的固态THz源,研究波导结构对激射光特性和远场光束质量的影响,是THz QCL设计中的关键。本文采用有限元方法对THz QCL双面和单面金属波导结构的限制和损耗特性进行分析,给出了限制因子、波导损耗和阈值增益随波导结构、激射波长等参数的变化关系。仿真实验结果表明:与单面金属波导相比,双面金属波导对光具有更好的限制作用,损耗也比较小,更适合做有源区的波导限制结构。在计算出波导中光场分布的基础上,又利用矢量衍射理论分析了THz QCL的光束质量,给出了不同波导宽度时出射光束的远场光束宽度和远场发散角,从应用方面为QCL的设计提供了一定参考。     

Electromagnetic coupling of coplanar waveguides and microstriplines to highly lossy dielectric media

The spectral-domain technique is utilized to analyze the coupling characteristics of coplanar waveguides and microstrip lines coupled with multilayer lossy dielectric media. Numerical results illustrating the dispersion characteristics of coplanar and microstrip lines, as well as the various electric field components coupled to highly lossy dielectric media, are presented. It is shown that the presence of a superstrate of lossless dielectric between the coplanar waveguide and the lossy medium plays a key role in setting up an axial electric field component that facilitates leaky-wave-type coupling to the lossy medium. The thickness of the superstrate relative to the gap width in the coplanar waveguide is important in controlling the magnitude of this axial electric field component. The coupling characteristics of the microstrip and coplanar lines are compared, and results generally show improved coupling if coplanar waveguides are utilized. Values of the attenuation constant α are higher for coplanar waveguide than for microstrip line, and for both structures α decreases with frequency     

Dispersionless and slow unidirectional air waveguide

Unidirectional waveguides and slow light waveguides both play the key roles in the modern communication system. The unidirectional waveguides do not support slow light. The traditional slow light waveguides are always limited to the group velocity dispersion. To combine both the functionalities of unidirectional transmission and slow light into one waveguide, we add a surface defect into unidirectional waveguide to modulate the odd mode dispersion. Through a structure optimizing, a dispersionless and slow unidirectional waveguide is obtained. The waveguide with compound functionalities is confirmed through the frequency-domain and time-domain simulations.     

基于太赫兹片上系统微带线的设计与仿真

太赫兹片上系统是一种将太赫兹产生和探测装置以及波导传输装置集成在同一基片上的设计,应用于晶体材料的共振吸收以实现对太赫兹时域光谱的探测。太赫兹产生与探测装置都由光电导天线构成,波导传输装置由微带线构成。微带线是一种能够传输高频电磁波的波导结构,但相比于自由空间波导具有高损耗和散射特性。为了研究微带线的结构参数对太赫兹波传输损耗的影响,采用模拟仿真的方法,得出了传输损耗随着传输长度和频率的增加而增加,随着微带线金属层厚度与介质层厚度的增加而减少的规律,从而证明了传输损耗的减少能够通过合理设计微带线结构来实现。     

镀膜刻槽型太赫兹聚合物波导管的传输特性研究

设计了外壁镀金膜环形槽型和内壁镀铜膜螺旋槽型两种太赫兹聚合物波导管。主要分析和比较这两种波导管的衰减与色散特性。在太赫兹频段,外壁镀金膜环形槽型比内壁镀铜膜螺旋槽型对太赫兹波的衰减大;内壁镀铜膜螺旋槽型比外壁镀金膜环形槽型的色散大,并且出现负色散现象。研究表明,内壁镀铜膜螺旋槽波导管适合传输太赫兹波,而太赫兹波在外壁镀金膜环形槽波导管内损耗较大,不适宜传输。分析二者的电场和磁场特性,均没有出现仿表面等离子体现象。     

THz interconnect with low-loss and low-group velocity dispersion

We report the demonstration of a physically flexible, practicable THz interconnect with minimal pulse distortion and loss. The interconnect is a parallel-plate waveguide, with the TEM mode excited, constructed of two thin copper strips. The incoming 0.22 ps THz pulse broadens to 0.39 ps after propagating 250 mm in the waveguide and is also attenuated by a factor of ten. We show that this attenuation is mainly due to the finite conductivity of copper with some additional loss caused by the beam spread in the unguided dimension. The pulse broadening is due to the frequency-dependent loss since the group velocity dispersion is negligible     

Time-domain wavelet Galerkin modeling of two-dimensionalelectrically large dielectric waveguides

The time-domain wavelet-Galerkin method based on Daubechies' compactly supported scaling functions of high regularity has been applied to the analysis of two-dimensional dielectric slab waveguides that have typical dimensions and material parameters of optical integrated waveguide components, and the results are compared with those obtained with the conventional finite-difference time-domain method. It has been found that the proposed method allows discretization with a much coarser grid than the conventional time-domain analysis techniques due to its local sampling and highly linear numerical dispersion properties. A series of numerical experiments demonstrates the capability of the method to simulate the wave propagation of electrically large inhomogeneous media with reduced computational expenditure     

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。