高阶体模准光模式激励器的设计与实验

基于开放式谐振腔及准光学模式变换理论,设计并实现了一种应用于回旋管振荡器冷测的高阶模式激励器。以140 GHz、TE_28,8模工作为例,通过计算机编程控制三维移动测量平台和网络分析仪完成了相应的实验测量。当模拟仿真获得在谐振腔激起频率为140.179 GHz、Q值为855、输出场分布与TE_28,8模的相关性为90.9 %时,对应设计构建模式激励器完成的冷测结果频率为140.155 GHz、Q值为876、横向电场明显具有TE_28,8的特征,为回旋管振荡器研究和设计过程检验提供了一个有效的实验平台。     

双共焦波导回旋行波管高频结构的电磁特性研究

研究了双共焦波导回旋行波管高频结构的电磁特性。根据惠根斯原理的光衍射理论,分析得出双共焦波导中的两类本征模式（叠加模和环形模）对应的截止频率和场分布情况。理论分析结果与商用仿真软件CST的仿真结果一致。其中用作回旋行波管工作模式的“反相叠加TE₀₆模”的损耗明显小于其他模式,这种不同模式损耗不同的特性将有效抑制竞争模式带来的寄生振荡。双共焦波导的模式密度略大于传统单共焦波导的模式密度,但是明显小于圆波导的模式密度,因此双共焦波导适合用作回旋行波管的高频结构。     

螺旋波纹波导中的返波

从螺旋波纹波导的一般性耦合波传输方程出发,根据螺旋波纹波导的模式耦合规则给出该波导内返波的耦合波方程和色散方程并分析其色散特性,由此分析螺旋波纹波导返波管的工作机理,并通过耦合波理论计算出本征模式中场的分布情况.     

可调谐氮化硅波导微环谐振腔滤波器研究

设计并制备了一种基于热光效应的集成可调谐氮化 硅(Si₃N₄)波导微环谐振腔滤波器,通过采用马赫-曾德干涉仪(MZI)构成的可调谐 耦合器控制耦合区耦合比,以实现滤波器消光比的调谐。设计并优化了微环谐振 腔的波导截面尺寸、弯曲半径和耦合区波导间隔等参数,并通过光刻、反应离子刻蚀(RIE )等工艺制备 了两种不同弯曲半径的Si₃N₄波导微环谐振腔。实验结果表明,本文器件在波长1550nm附近处的自由光谱 范围(FSR)为68pm,3dB带宽约为16pm,品质因子Q达到了9.68×10 4,消光比可调范围约为17dB。     

具有亚波长模式局域性的全介质反槽波导及其与输入/输出光纤的高效耦合

由于金属固有的欧姆损耗,表面等离子体波导通常具有较大的传输损耗。基于此,提出了一种全介质反槽波导结构,该波导可以同时实现亚波长模式局域性和理论上无损耗的传输,归一化模式面积可以达到3.4×10^-2。另外,为了实现该小尺寸反槽波导与输入/输出光纤的高效耦合,提出了一种高效的耦合方案,耦合效率可以达到92.7%,在y和z方向上1 dB损耗的耦合偏差均约为2 μm。     

Ku波段螺旋波纹波导回旋行波管色散特性研究

为抑制回旋行波管的自激振荡和增加回旋行波管带宽,俄罗斯G.Denisov等人提出一种新型回旋行波管结构——螺旋波纹波导回旋行波管。通过螺旋波纹波导的特殊结构使通过波导的两种模式发生耦合,耦合出一种新的工作模式,从而改变色散特性,达到抑制自激振荡和增加带宽的目的。通过螺旋波纹波导的色散方程,分析其色散曲线,从而分析螺旋波纹波导作为回旋行波管高频系统的优势。     

基于柱矢量模式的光纤迈克尔逊传感特性研究

基于涡旋光纤(vortex fiber,VF) 激发的柱矢量模式(cylindrical vector modes,CVMs) 设计了迈克尔逊干涉仪传感器,并对轴向应变、温度和折射率传感特性进行了理论研究和实验验证。 通过对VF施加一个微弯长周期光栅(microbend long period gratings,MLPG),激发一阶CVMs(TE₀₁、HE₂₁和TM₀₁);在VF尾端加反射镜,反射后纤芯中的基本模式HE₁₁与环芯中的CVMs产生干涉,构成了迈克尔逊干涉仪。实验测得对应于柱矢量模式TM₀₁、HE₂₁和TE₀₁的应变灵敏 度分别为-1.1 nm/mε、-1.1 nm/mε和-2.1 nm/mε,温度灵敏度分别为9.3 pm /℃,3.4 pm /℃和-2.4 pm /℃,而折射率不敏感。该传感器结构简单,且TE₀₁模式具有最高应变灵敏度和最低温度灵敏度,可作为折射率不敏感的、温度交叉灵敏度低的理想无补偿应变传感器,是智能型工程结构中下一代传感器的理想选择。     

螺旋波纹波导在高功率微波领域中的应用研究

螺旋波纹波导是一种具有特殊结构的高功率微波源波导结构,螺旋波纹波导的特殊结构使得TE11和TE21两模式在角向耦合,耦合出的新工作模式具有良好的色散特性和模式选择特性,因此该波导具有广泛的应用价值。简要地介绍了螺旋波纹波导的结构原理,概述了该波导在高功率微波领域的工作原理。通过分析和模拟计算表明,螺旋波纹波导在高功率微波源中极具发展潜力,值得进一步研究。     

高Q值横向激发体声波谐振器的设计与制备

随着5G移动通信时代的发展,射频前端(RF front-ends)的滤波和信号处理迫切需要高频大带宽的声学谐振器。横向激发体声波谐振器(XBAR)具有超高的工作频率和超大的机电耦合系数(k²),但其品质因数(Q)值不高,阻碍了其在射频前端中的应用。该文提出了一种基于ZY切铌酸锂(LiNbO₃)的XBAR谐振器,通过有限元(FEM)仿真对谐振器进行了优化设计,并在微机电系统(MEMS)工艺下对谐振器进行加工。该文所制备的横向激发体声波谐振器A₁模式的谐振频率为4.72 GHz,k²=26.9%,Q_{3 dB}为384,温度频率漂移系数为-60.5×10^-6/℃。A₃模式的谐振频率为13.5 GHz,k²=4.4%。     

基于高Q值Si3N4片上光学微腔的孤子光频梳

高Q值片上微腔已被证明是一种性能优异的克尔孤子光学频率梳产生平台。由片上多模波导构成的Si₃N₄微腔可以同时实现产生暗孤子所必须的高品质因子和反常色散。为了进一步降低产生单孤子光频梳的阈值功率,文章设计了一种具有欧拉弯曲的新型跑道型Si₃N₄微腔,与传统的圆形弯曲波导相比,跑道型微腔直波导连接处弯曲半径的突然变化被显著抑制,这抑制了高阶模式耦合并降低了传播损耗,从而获得了超过5×10⁶的品质因子。基于该新型微腔,使用辅助激光加热方法仅用47mW泵浦激光器(估计片上泵浦功率为33mW)就产生了重复频率在Ka波段且带宽超过20nm(对应于129fs的脉冲持续时间)的单孤子微腔光频梳。     

Linear Analysis of a Cyclotron Autoresonance Maser (CARM) Operating in a Transverse Magnetic Mode

In the fast-wave devices like gyrotron, gyro-peniotron and cyclotron autoresonance maser (CARM) that generate millimeter and sub-millimeter waves, the transverse dimensions of the resonator and the output cylindrical waveguide become small. In order to prevent loss of electrons and thermal loading of the rf structure, the electron beam must be kept relatively far from the walls. The latter requirement demands smaller transverse dimensions of the helical electron beam as well. In this paper linear formulation of a CARM operating in a general transverse-magnetic (TM) mode is derived, and a detailed analysis of the influences of the parameters is presented for the TM_1,1 mode CARM. It is found that, compared to the TE_1,1 mode which is often employed in gyrotron traveling wave tube (gyro-TWT) and CARM experiments, the TM_1,1 mode has a greater eigen value and consequently leads to a greater waveguide radius for a given cutoff wave number, and also, allows the electron beam to be settled close to the waveguide axis to have a small transverse dimension. Results show that a TM-mode CARM can reach high power and ultrahigh gain, just as a TE-mode CARM or a TE-mode gyro-TWT does.     

Nonlinear Simulation of a Cyclotron Autoresonance Maser (CARM) Operating in a Transverse Magnetic Mode

In the gyrotron operation, the transverse-magnetic (TM) mode is excluded because the TM mode instability vanishes when the vacuum waveguide mode and the beam mode are at grazing incidence. However, situation changes in a cyclotron autoresonance maser (CARM) interaction. In this paper nonlinear formulation of a TM-mode CARM is derived, and detailed simulations are presented for the TM_1,1-mode CARM. Simulation results show that a TM_1,1-mode CARM can reach high power of megawatts and ultrahigh gain of more than 70 dB, as a TE_1,1-mode gyrotron traveling wave tube (gyro-TWT) and TE_1,1-mode CARM did in the reported experiments.     

Rippled wall mode converters for circular waveguide

We present the general theory of rippled wall mode converters. Coupling coefficients for TE and TM waves, of both fixed and rotating polarizations, are calculated. The waveguide ripples considered may be axisymmetric, fluted or helical. We describe in detail a 97% efficient TE₀₄/TE₀₁ converter designed for use with a 35 GHz gyrotron. Cold test results confirm its performance.     

On the kinetic theory of electron cyclotron maser

This paper starts from the kinetic theory to expound the method of characteristics. Influence of the equilibrium distribution functionf ₀ upon analyzed result is fully investigated. The dispersion equation is regorously derived in a waveguide coordinate system in case of interaction between TE _mn field in a circular waveguide and a single-momentum ring-shaped electron beam. In the meantime, we make some critical review of previous papers and clarify their confusion and ambiguities.     

Mode converters from TEom ○ to TE m0 □ for high-power applications in the frequency range 1 to 30 GHz

A mode converter is described for transitions from circular symmetric modes TE_om ^○ to rectangular waveguide modes TE _m0 ^□ and vice versa. This converter conserves the power of all circular symmetric modes emitted by a gyrotron and aligns the fields into linearly polarized modes required for effective plasma heating. Suitable combinations of waveguide diameter and number of sectors dividing (or combining) the power avoid the excitation of unwanted modes.     

Undesired resonances in oversized rippled-wall mode converters

A new method to study rippled-wall mode converters based on a generalized investigation of multi-resonance phenomena in periodically perturbated circular oversized waveguides is presented. These resonances cause serious problems in the design of advanced, very high-power millimetre wave mode converters. The concept of a mode diagram helps in the initial design steps to get a global feel for possible resonances at each frequency and waveguide diameter. The optimal conversion path is determined from this mode diagram to avoid unwanted mode resonances. This method is shown applied to a TE_0.1?TE₀₃converter with a waveguide diameter of 27-79mm working at 60GHz. This converter is very close to the worst resonance effect (first-order resonance: |β₀₃? β₀₄.| ≈| β₀₃? β₀₁ |) which destroys totally the desired conversion effect. The second example shown is a TE₀₂?TE₀₁ converter with a waveguide diameter of 44-45 mm working at 28 GHz. In this case the resonance effect is of second order (i.e. | β₀₂? β₀₃|≈2| β₀₁? β₀₂|).     

Mode selective directional couplers for overmoded waveguide systems

Two types of directional couplers for transverse electric (TE) modes are described: short and multihole couplers, respectively. They selectively pick one mode out of a mode mixture in an overmoded circular waveguide system. Unwanted modes are either statistically kept at low level or are suppressed by destructive interference in the coupling waveguide. Mode selectivity and directivity in multihole couplers oscillate up and down with an increasing number of holes, finally reaching a minimum of approximately 20 dB, unless there are competing modes with rational fractions of the beat wavelength. A multihole coupler for the TE₀₂ mode (28 GHz, 63.4 mm waveguide diameter, 41 holes) and a length of 1.6 m shows a calculated directivity of 68 dB and suppresses the unwanted modes TE₀₁ with 34 dB (24 dB), TE₂₂ with 37 dB (45 dB), and further modes TE_?m (?<5, m<6) with 17 dB to 34 dB in forward direction (figures in parentheses are for unwanted modes propagating in backward direction). A short directional coupler for the TE₀₁ mode (28 GHz, 63.4 mm waveguide diameter) with 16 holes and a length of 230 mm shows a directivity of 55 to 100 dB between 27.9 and 28.1 GHz, suppressing the TE₀₂ mode with 35 to 80 dB, the TE₀₃ mode with 30 to 65 dB, and the TE₂₂ mode with 30 to 70 dB.     

High-power millimetre-wave mode converters in overmoded circular waveguides using periodic wall perturbations

This work reports on measurements and calculations (coupled mode equations) on the conversion of circular electric TE_0n gyrotron mode compositions (TE₀₁ to TE₀₄) at 28 and 70 GHz to the linearly polarized TE₁₁ mode by means of mode converter systems using periodic waveguide wall perturbations. Mode transducers with axisymmetric radius perturbations transform the TE_0n gyrotron mode mixture to the more convenient TE₀₁ mode for long-distance transmission through overmoded waveguides. Proper matching of the phase differences between the TE_0n modes and of lengths and perturbation amplitudes of the several converter sections is required. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TE₀₁ mode into the TE₁₁ mode which produces an almost linearly polarized millimetre-wave beam needed for efficient electron cyclotron resonance heating (ECRH) of plasmas in thermonuclear fusion devices. The experimentally determined TE_0n -to-TE₀₁ conversion efficiency is (98 ± 1)% at 28 and 70 GHz (99% predicted) while the TE₀₁-to-TE,, converter has a (96 ± 2)% conversion efficiency at 28 GHz (95% predicted) and (94 ± 2)% at 70 GHz (93% predicted) with ohmic losses included in each case. This paper also presents theoretical and experimental results on the two-step TE₁₆-to-TE₁₂-to-TE₁₁ mode conversion at 28 GHz by means of two periodically rippled-wall mode converters. The conversion efficiencies achieved are almost 92% and 95%, respectively. Similar converters might be used for transformation of the output modes of future high-frequency TE_1n gyromonotrons or 10 GHz gyro-klystron amplifiers into the TE₁₁ mode, which in turn can then be transformed by circumferentially corrugated or dielectrically coated mode transducers into the perfectly linearly polarized quasi-optical HE₁₁ hybrid mode. The efficiency of periodically modulated wall mode-converters can be considerably improved by proper re-matching of the phase difference between the two converted modes within the converter.     

Experimental Study of a Slot Antenna Excited by a TE011 Mode Coaxial Cavity

A slot antenna is developed to excite the high harmonic waveguide mode for generating large-area plasmas. This antenna consists of a TE₀₁₁ mode coaxial cavity with the axial slots positioned on equal interval on the inner wall. The waves radiated from those slots can excite the high harmonic mode in the central area. With the azimuthal symmetric wave field of the TE₀₁₁ mode, the number of the slots can be chosen to match the field pattern of the high harmonic mode. In this report, the dispersion relation of the coaxial waveguide, the coupling scheme and the mode competition of the cavity are studied. A method has been successfully developed to suppress the TE₁₂₁ mode which is the most competing mode to the TE₀₁₁ mode.     

Demonstration of a High-Order Mode Input Coupler for a 220-GHz Confocal Gyrotron Traveling Wave Tube

A design of high-order mode input coupler for 220-GHz confocal gyrotron travelling wave tube is proposed, simulated, and demonstrated by experimental tests. This input coupler is designed to excite confocal TE ₀₆ mode from rectangle waveguide TE ₁₀ mode over a broadband frequency range. Simulation results predict that the optimized conversion loss is about 2.72 dB with a mode purity excess of 99%. Considering of the gyrotron interaction theory, an effective bandwidth of 5 GHz is obtained, in which the beam-wave coupling efficiency is higher than half of maximum. The field pattern under low power demonstrates that TE ₀₆ mode is successfully excited in confocal waveguide at 220 GHz. Cold test results from the vector network analyzer perform good agreements with simulation results. Both simulation and experimental results illustrate that the reflection at input port S11 is sensitive to the perpendicular separation of two mirrors. It provides an engineering possibility for estimating the assembly precision.