Design of a Quasi-Optical Mode Converter for a Frequency Step-Tunable Gyrotron

The quasi-optical mode converter for a frequency step-tunable gyrotron which consists of a dimpled-wall antenna (Denisov-type launcher) and a beam-forming mirror system has been optimized for 9 modes from TE_17,6 at 105 GHz to TE_23,8 at 143 GHz. The first mirror is a large quasi-elliptical focusing one; the second and third are phase-correcting mirrors with a non-quadratic shape of the surface. The results of calculations show that for these modes the Denisov-type launcher has a well-focused beam with low diffraction losses, and the radiation pattern presents an almost identical field shape for all modes considered. A multi-mode optimization of the phase-correcting mirrors with two different methods has been tested. The simulations show that the phase-correcting mirrors can be used for broadband operation in the frequency range from 105 GHz up to 143 GHz in the various design modes. This quasi-optical mode converter can achieve efficiencies of 94%-98% for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode.     

Investigation of a Broadband Quasi-Optical Mode Converter for a Multi-Frequency 1 MW Gyrotron

A broadband quasi-optical (QO) mode converter for a multi-frequency gyrotron has been designed and tested at Forschungszentrum Karlsruhe (FZK). The launcher is optimized for the TE_22,8 mode at 140 GHz, but the radiated beams present an almost identically focused pattern for all 9 considered modes between 105 GHz (TE_17,6) and 143 GHz (TE_23,8). Combining with a beam-forming mirror system, which consists of a quasi-elliptical mirror and two phase-correcting mirrors with non-quadratic surface contour, further calculations show that efficiencies of more than 94% have been achieved for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode. Low power (cold) measurements show a good agreement with theoretical predictions. This QO mode converter can be used for the broadband operation of a multi-frequency 1 MW gyrotron.     

A Quasi-Optical System for Converting TE0n Mode Outputs of a Gyrotron into Gaussian Beams

In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into Gaussian-like beams. It consists of a quasi-optical antenna, two focusing mirrors and a filter which removes the side lobes of the beam. The system is appropriate as a transmission line for frequency tunable gyrotrons operating at TE_0n mode. As an illustration of our approach, we present results which demonstrate the applicability of the developed system for conversion of the radiation generated by the Gyrotron FU IVA. The examples include conversion of three TE_0n modes (TE₀₂, 223 GHz; TE₀₃, 323 GHz; TE₀₄, 423 GHz) into Gaussian- like beams.     

紧凑型宽带TE01-TE02模式转换器

在传播常数随半径变化的情况下近似分析了两模转换条件,得到了模式转换器的初始结构,然后调用迭代法进行优化,最终能得到结构紧凑、带宽较宽、转换效率高的模式转换器。设计了两周期的Ka波段和一周期的W波段TE01-TE02模式转换器,带宽（转换效率95%以上频带宽度）分别达到2.47,8 GHz。CST仿真结果与耦合波仿真程序计算结果吻合较好,验证了该方法的有效性。     

Design of a Quasi-Optical System to Convert TE0n Mode Outputs of a Gyrotron into Gaussian Beams

In this paper we present a novel design of a quasi-optical system for conversion of gyrotron outputs into gaussian beams. It consists of a quasi-optical antenna, four focusing mirrors (parabolic cylinders) and a filter which removes the side lobes of the beam. The system is capable to convert three TE_0n mode outputs into gaussian beams with waist size of 16.7 mm as well as four TE_1n mode outputs into bi-gaussian beams with waist size of 10.9 mm in width and 16.5 mm in length.     

V波段圆波导TE_(01)模式激励器

V波段圆波导TE01模式激励器由矩形TE10模式到矩形TE20模式变换器和矩形TE20模式到圆波导TE01模式变换器组成。采用H面(磁面)转弯激励的方式实现矩形TE10模式到矩形TE20模式的变换;根据圆波导TE01模式的场分布特性,引入过模波导实现了矩形TE20到圆波导TE01的变换。计算结果表明设计的激励器转换效率在95%以上;模式纯度在98%以上的相对带宽可达4.2 GHz;其中在43.4 GHz处的最大转换效率为99.08%,纯度为99.20%。     

Ka波段TE01模回旋速调管输出腔

 利用模式展开和场匹配理论,建立了具有突变结构谐振腔的散射矩阵。在此基础上编制了FORTRAN计算程序,并对Ka波段TE₀₁模回旋速调管的具有突变结构的开放式输出腔进行了数值计算。分析了回旋速调管输出腔的腔体长度和半径变化,以及输出耦合孔的半径和厚度变化对输出腔的品质因数和频率的影响。结果表明：由程序模拟输出腔所得到的计算结果与HFSS软件的结果一致;与冷测实验结果相比,品质因数的相对偏差为1.65%,谐振频率的偏差为10 MHz。     

高功率TE_(01)过模斜接弯头设计

设计并分析了TE01斜接弯头结构,该结构由两段相同且垂直的模式变换段及与模式变换段呈45°斜接的金属镜面组成。整个结构等效于两个模式变换段对接,但中间存在间距为波导直径的缝隙。模式变换段将纯TE01模式转换为TE01和TE02的混合模式,该混合模式在缝隙中传播时电场呈现对称分布,从而降低了模式转换损耗,提高了传输效率。对设计的Ka波段TE01斜接弯头结构的理论仿真和加工实测结果表明:中心频点转换效率在98%以上,在2 GHz带宽内传输效率95%以上,插损小于0.2 dB,驻波小于1.2。     

圆波导TM_(01)-矩形波导TE_(10)模式转换器

设计了一种高功率圆波导TM01-矩形波导TE10模式转换器,可以实现圆波导TM01模式与矩形波导TE10模式之间的相互转换。仿真结果表明:中心频率为9.7GHz时该模式转换器转换效率大于99.99%,回波损耗小于-40dB,转换效率大于90%时的带宽大于0.4GHz。调节底面短路圆波导长度可以实现模式转换器在9.2~10.1GHz范围内调谐(模式转换效率大于99%)。在圆波导和耦合段连接处引入倒角可有效降低场强,提高功率容量,注入功率0.7GW,其表面场强小于1 MV/cm。     

Numerical Simulation of Waveguide TM01-TE11 Mode Converter Using FDTD Method

We study a transmission problem of an electromagnetic pulse with given transversal structure passing through a waveguide converter from TM₀₁ to TE₁₁ mode of circular waveguide. Using FDTD numerical simulation method we have investigated mode structure of the pulse at the output of the converter and its dependence on pulse length at the input. Also we have obtained frequency characteristic by calculating Fourier response for a pulse with wide spectrum.     

Effects of Beam and Magnetic Field Parameters on Highly Competing TE01 and TE21 Modes of Vane Loaded Gyro-TWT

In this paper, the dispersion relation for a vane-loaded cylindrical waveguide, considering the azimuthal harmonic effects arising from the azimuthal periodicity of the vanes, excited in transverse electric (TE) modes and the gain for a gyro-TWT have been presented. The effects of beam and magnetic field parameters on two highly competing modes have been studied.     

Equivalent step-index profile for graded W-fibres: application to TE01 mode cut-off

Snyder's equivalent step-index method is extended to the case of graded profiles with a depressed cladding. This method is then used to determine the limit of monomode operation. Comparison with the results obtained by an exact numerical technique is made for a large variety of simulated profiles, including those with ripples in the cladding. Conclusions are drawn concerning the sensitivity of various profile-shapes to such ripple structure. The method is applied also to measured profiles, reconstructed by a well-known tomographic procedure. In this latter case a comparison is made with experimentally determined values.On leave from CNET, Lannion, France.     

一种新型光学模式转换器

提出了一种梯度折射率分布介质为基质的单体光学模式转换器,可以将两正交截面内瑞利长度相同、光腰重合的厄米-高斯光束转换为拉盖尔-高斯光束.这种转换器具有一体化且只有两个反射面的特点,因此易于调整、光能反射损耗小;对于两正交截面内瑞利长度不同、光腰不重合的厄米-高斯光束,提出了一种可调节其瑞利长度和光腰位置的光腰调节器,将光腰调节器与单体光学模式转换器组合使用,也可以将这种厄米-高斯光束转换为拉盖尔-高斯光束.     

基于微变形反射镜的TEM00模式控制

分析了连续面形薄膜微变形反射镜的结构,提出了一种简化的变形镜球面分析模型,用该模型分析含有变形镜的谐振腔,导出了TEM00模式强度与曲率半径的严格表达式,并使用Matlab软件对其进行了仿真分析.结果表明增大变形镜的曲率半径能够增大TEM00模式的输出强度.搭建含有变形镜谐振腔的实验光路系统来控制TEM00模式输出,观测到类似的输出变化.     

Quasi-Optical Sub-Doppler Lamb-Dip Spectrometer

Radiophysics and Quantum Electronics - We describe a new sub-Doppler spectrometer with an enlarged gas cell, which was created at the IAP RAS for high-precision laboratory measurements of molecular...     

Multiple Diodes Quasi-Optical Oscillater

This paper presents quasi-optics techniques, millimeter techniques and a global optimization method etc techniques. It is a structure of quasi-optics power combiner, that includes a spherical reflection, that the radius of the curvature is R and another one is a hybrid reflector that is called input reflector. The space of the both reflectors is LL. The monolithic source-array is made up of 25 Gunn diodes that are mounted of parallel brass bars that have low thermal resistance. And the bars are fixed on the inner plane surface of the hybrid reflector. The hybrid reflector made up of a plane and a spherical, that the radius of the curvature are R. It is designed that higher fundamental mode power, larger fractional power of fundamental mode power and more combining efficiency of the quasi-optics power combiner.This paper describes an algorithm, which can determine the global optima of the power combiner of solid-state millimeter wave resonator. The global optimization method can determine a neighborhood of the global optima of an objective function and an estimation of the global optima. In the quasi-optical resonator, the objective functions are the fundamental mode power, the fractional power of fundamental mode and the combining efficiency respectively.     

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE₀₁ circular waveguide mode into the TE₁₀ rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.     

High-Efficient Mode Converter for ITER Gyrotron

A high-efficiency mode converter of the ITER gyrotron operating mode into the Gaussian wave beam has been developed. It includes an irradiating waveguide with shallow deformation and profiled quasi-optical mirrors to increase the Gaussian content. Low-power tests were carried out with a TE_25.10 mode exciter and a mode converter. A prototype of the short-pulsed 170 GHz gymtmn with the new converter was manufactured and tested. Diffraction losses measured inside the tube were less then 2% at the 1 MW power level. A high Gaussian mode content in the output beam has been also demonstrated.     

A Single-Ridged Coaxial Hybrid TE011 Coupler with High Mode Purity

We design a single-ridged coaxial hybrid coupler which excites a TE₀₁₁ mode of high mode content in a cylindrical cavity, resonating at 28.2GHz. The coupler consists of a WR-28 rectangular waveguide, a coaxial TE_n11 cavity, and a cylindrical TE₀₁₁ cavity. Both TE₃₁₁ coaxial cavity and TE₄₁₁ single-ridged coaxial cavity are analyzed to examine the TE₀₁₁ mode purity in the central cavity. Mode purity analysis is performed by a field expansion method using Fourier-Bessel orthonormal basis functions. Numerical calculations predict that the TE₄₁₁ single-ridged coaxial cavity excites the TE₀₁₁ mode with mode purity of 98.6%, which is improved by 3% higher compared with the TE₃₁₁ coaxial cavity. Measurements on the single-ridged coaxial coupler show a resonant frequency at 28.078GHz and ohmic and external Qs of 1560, 473 respectively, which are in good agreement with the simulated results of a 3-D finite element electromagnetic code.     

TE-TM Mode Converter Using Optically Active Polymer

A novel TE-TM mode converter using optically active polymer: poly-1-menthylmethacrylate (PMtMA) was studied theoretically and experimentally. In a three-layered slab waveguide consisting of the PMtMA core layer on a fused quartz substrate, a low-loss TE₀-TM₀ mode conversion with an efficiency of 60 to 70% was easily obtained for the first time at a wavelength of 441.6 nm. The method to achieve a phase-matched operation of this polymer TE-TM mode converter was also discussed.