Waveguide tapering for beam-width control in a waveguide transducer

In a waveguide transducer that transmits an ultrasonic wave through a waveguide unit to a test structure, it is most preferred to send a non-dispersive ultrasonic wave of a narrow beam width. However, there is an unresolved conflict between the generation of the non- or less-dispersive wave and the transmission of a narrow-beam wave into a test structure. Among others, the thickness of the waveguide unit in a waveguide transducer is the key variable determining these two conflicting criteria, but the use of a uniformly-thick waveguide of any thickness cannot fulfill the two conflicting criteria simultaneously. In this study, we propose a specially-engineered tapered waveguide unit for the simultaneous satisfaction. An excitation unit is installed at the end of the thin region of the tapered waveguide and generates only the lowest non-dispersive shear-horizontal wave. Then the generated wave propagates through the tapered region of the waveguide unit and reaches the thick region of the waveguide with insignificant mode conversion to higher modes. If the tapered waveguide is used, the surviving lowest mode in the thick region of the waveguide is shown to carry most of the transmitted power and is finally propagated into a test structure. Because the beam size of the propagated wave and the thickness of the contacting waveguide region are inversely related, the thick contacting region of the tapered waveguide ensures narrow beam width. Numerical and experimental investigations were performed to check the effectiveness of the proposed waveguide-tapering approach.     

Absorption Measurement Using a Leaky Waveguide Mode

We propose an optical waveguide sensor using a leaky mode for absorption measurement of liquid samples. This sensor uses a single coupling prism. A cladding layer and a waveguide layer are directly deposited on the reflecting surface of the prism. The intensity of the internally reflected beam at an appropriate incident angle is very sensitive to the imaginary part of the sample attached to the surface of the waveguide layer. The sensitivity of this sensor is controlled by the thicknesses of both cladding and waveguide layers. We studied the performance of the sensor by numerical calculation.     

Integral Representations of a Pulsed Signal in a Waveguide

Acoustical Physics - The problem of pulsed excitation of an acoustic waveguide with a constant cross section is considered. Absorption is ignored. As the most general model of such a waveguide,...     

Generation of a Plasma Waveguide with Slow-Wave Structure

Using the particle-in-cell simulations,we report an efficient scheme to generate a slow wave structure in the electron density of a plasma waveguide,based on the array laser-plasma interaction.The spatial distribution of the electron density of the plasma waveguide is modulated via effective control of the super-Gaussian index and array pattern code of the lasers.A complete overview of the holding time,and the bearable laser's intensity of the electron density structure of the plasma waveguide,is obtained.In addition,the holding time of the slow wave structure of the plasma waveguide is also controlled by adjusting the frequency of the array laser beam.Finally,effects due to ion motion are discussed in detail.     

Hybrid Modes in a Square Corrugated Waveguide

By using two scalar eigenfunctions, electric and magnetic fields in the rectangular (or square) corrugated waveguide are analyzed. In a rectangular corrugated waveguide, the boundary conditions on two corrugated and two smooth walls can be satisfied to excite the hybrid mode. In a highly oversized waveguide where the wavelength of dominant mode is close to that in vacuum, two smooth walls can be exchanged with the corrugated walls because the boundary condition at those walls is satisfied approximately. The replacement is possible due to almost no penetration of the electromagnetic fields into the gap of the replaced walls when the direction of main electric field is parallel to the gap of replaced walls. This characteristic enables us to rotate the polarization of the hybrid mode in the oversized square waveguide with all four corrugated walls and is applicable to the remote steering antenna for electron cyclotron heating in the ITER.     

一种温度不敏感型阵列波导光栅的研究

研究了的一种新型温度不敏感型阵列波导光栅(AWG)。该新型温度不敏感型阵列波导光栅的波导采用混合材料的波导结构，该混合材料波导通过在石英波导芯层上旋涂聚合物材料的上包层，达到改变波导温度特性的目的，使得阵列波导光栅的温度敏感性降低。通过理论分析和有限差分方法研究了其中两种结构：三层混合材料波导构成的阵列波导光栅和四层混合材料波导构成的阵列波导光栅，计算了该新型温度不敏感型阵列波导光栅的温度特性。结果表明，在一定的设计下，温度变化0～50℃时，这两种温度不敏感型阵列波导光栅的最大波长漂移量小于0．03nm，不到无温度控制时常规阵列波导光栅最大波长漂移量的4％。     

Synchrotron Radiation in a Circular Metallic Waveguide

We study theoretically the influence of a circular metallic waveguide with a longitudinal magnetic field on the synchrotron radiation of a point electric charge moving along a helical trajectory coaxial with the waveguide axis. The main attention is focused on the analysis of the energy characteristics of radiation of electromagnetic E and H waves. We derive the formulas for the radiation powers of E and H waves. It is shown that, under certain conditions, slowly moving electric charges do not radiate any of these electromagnetic waves in the circular waveguide.     

Control of Two-Photon Transport in a One-Dimensional Waveguide

We study the system consisting of a one-dimension waveguide side-coupled to a nonlinear cavity which was doped with a lambda-type atom and investigate the control of photons transport in one-dimension waveguide through manipulating the atom contained in the cavity. Employing the polariton technique, we show that in the single-photon case, the system behaves as a waveguide coupled to a two-level system. By solving the Schr?dinger equation, we show that single photon switch can be achieved by tuning the Rabi frequency of the classical field. In the two-photon case, the system behaves like a waveguide coupled to a cascade three-level system. Two-photon quantum correlation in the position variation can be controlled by adjusting the Rabi frequency.     

硅基二氧化硅波导和SOI脊型波导应力双折射研究

采用有限元方法分析了硅基二氧化硅波导和SOI（Silicon on Insulator）脊型波导内部残留热应力引起的双折射.对于硅基二氧化硅波导,应力双折射系数的数量级为10－4,对于上包层为空气的SOI脊型波导,该系数的数量级为10－5,对于上包层为SiO2的SOI脊型波导,该系数的数量级为10－3,可见在硅基二氧化硅波导和上包层为SiO2的SOI脊型波导中产生了大的应力双折射,而在上包层为空气的SOI脊型波导中应力双折射较小.     

Magnetic-Type Waves in a Tapered Waveguide of Subwavelength Cross Section

The characteristics of electromagnetic waves in a narrowing waveguide are investigated. A method for field analysis is developed based on the application of transverse modes parametrically dependent on the longitudinal coordinate. For a circular cross section waveguide, a system of equations for the wave amplitudes is obtained, the waves being coupled owing to a variable tilt of the walls. It is shown that in the adiabatic approximation, there exist independent eigenwaves whose structure reflects the field energy density variation due to the waveguide radius variation. A detailed analytical and numerical investigation of these fields has been carried out for a waveguide with a special profile of hypergeometric type. The applicability of the adiabatic approximation is studied and conversion of the fundamental mode into higher-order modes is assessed. The amplitudes of the higher-order modes are obtained using the Green function for ordinary differential equations. The region of the waveguide parameters is found where the higher-order mode amplitudes are not great and the adiabatic approximation is highly accurate. The dependence of the transmittance of a semi-infinite waveguide on the input radiation characteristics is obtained. It is established that the field amplitudes at the waveguide output strongly depend on the wavelength of the input radiation, on its transverse structure, and the waveguide profile steepness. The greatest output fields take place in the case of an abrupt dependence of the waveguide radius on the longitudinal coordinate.     

Modal Characterization of a Planar Waveguide in Bismuth Borate Crystal

We report on the fabrication and modal property studies of planar waveguide structure in x-cut bismuth borate biaxial crystal formed by He ion implantation with triple energies. The prism coupling method is used to measure the effective refractive indices of this waveguide. We reconstruct the refractive index distribution of this waveguide by the reflectivity calculation method. Our results indicate that a broadened optical barrier is produced by the multiple He ion implantations. The so-called tunneling effect of the non-stationary mode in this type of barrier waveguide is presented by the well-known finite difference beam propagation method.     

光波导技术同步测量棱镜及波导薄膜参数

依据全反射理论和棱镜耦合原理,实现了对棱镜折射率及波导薄膜材料折射率和厚度的同步测量。使用高准直半导体激光器激光入射到棱镜内部与波导膜的分界面上,逐步旋转棱镜或改变棱镜的入射角,得到棱镜耦合M线,曲线前面几组的波谷为波导模激发,在M线左侧收尾处有一个不完整波峰,其反射光强随入射角迅速衰减,为全反射时的临界点,由此可实现棱镜及波导薄膜参数的同步测量;用此法测量了棱镜耦合一体化平面波导棱镜的折射率和聚甲基丙烯酸甲酯(PMMA)聚合物波导薄膜的折射率和厚度。测量棱镜折射率精度为±1.9×10-4,波导薄膜折射率和厚度的精度分别为±6.2×10-4 μm和±1.6×10-2 μm。     

Channeling of Neutrons in a Planar Waveguide

The propagation of neutrons in the middle layer of a planar waveguide in the form of a three-layer thin film has been investigated. The microbeam from the end face of the film has been registered. The neutron channeling length has been measured as a function of the thickness of the upper waveguide layer and the resonance order. The experimental data have been compared with theoretical results.     

Channeling of Neutrons in the Potential Well of a Planar Waveguide

The channeling of neutrons in a three-layer planar waveguide with a neutron-optical potential well is studied. Neutrons incident on a sample surface, which propagate in a middle layer and escape from the waveguide end in the form of a narrow divergent beam, are detected. The decay parameter of a neutron wave inside the waveguide is measured as a function of the potential well depth. Experimental results are compared with a theory.     

带有矩形过渡区的非对称Y分支光波导

提出了带有矩形过渡区的非对称Y分支光波导的两种设计方案。分别通过设置两分支波导不同的宽度和改变分支波导与矩形中心的轴偏移量,去获得非对称分支比。采用有限差分光束传播法（FD-BPM）对两种结构进行模拟,得出它们的分支比和损耗。分支比分别最高可达809／6和72．9％,其相对应的损耗分别低于0．12dB和0．23dB,充分证明了方案的可行性,为以后非对称Y分支光波导的制作提供了实验基础。     

Field Analysis of a Metal-Coated Planar Waveguide with Chiral Core

Eigenequations for a metal-coated planar chiral dielectric waveguide and a mirror-conjugate planar chiral dielectric waveguide are derived. The eigenequations are given in simple formulations. The results indicate that the perfect conductive (or magnetic) boundary can produce mirror-conjugate of chiral media and the left-handed and right-handed circularly polarized modes couple with each other due to the conductive boundary. The propagation characteristics of a metal-coated planar waveguide with chiral core are presented. An interesting phenomenon is observed that the field distributions vary with respect to the operating wavelength.     

Light Penetration through a Tapered Waveguide

An approximate pattern of calculation of the field behavior in waveguides of variable radius is proposed. It is based on the assumption of a slow dependence of the radius on the longitudinal coordinate and is reduced to the solution of an ordinary differential equation. The dependences of the waveguide transmission on the frequency of radiation, entrance and exit radii, as well as the rate of radius variation along the axis are studied. The analysis is carried out within the range of parameters typical for optical fibers used in optical near‐field microscopy. It is shown that the increase in the rate of radius variation with the longitudinal coordinate will cause the transmission coefficient of the tapered waveguide to increase.     

复合结构偏心对同轴波导电磁特性的影响

采用三维电磁仿真软件CST Microwave Studio,数值模拟了内外导体轴线复合结构偏心对同轴波导电磁特性的影响。结果表明:当内外导体的轴线同时存在平行偏心和倾斜偏心时,改变了波导的边界条件,从而导致同轴波导的S21参数和电场幅值实质性下降。随着复合结构偏心程度的加剧,同轴波导的S21参数和电场幅值减小越大。同时,复合结构偏心比平行偏心或倾斜偏心单独存在时对同轴波导电磁性能的影响更大。因此,在同轴波导的实际制作过程中,应尽力避免发生复合结构偏心。     

用圆对称截面波导逼近正多边形截面波导的方法

求解各类截面波导的本征方程,一直是导波光学研究的焦点问题。提出用内切圆和外接圆截面波导逼近正多边形截面波导的方法,把正多边形截面分为三个部分：内切圆以内,外接圆以外,以及介于它们之间的第三部分。根据各边界处电磁场切向分量相等的条件,得到了正多边形截面波导的传播方程和TE0n各模式的截止条件,在所给定的截面条件下,得出可以容纳的TE波模式数为22个。     

包含左手材料的四层平板波导中的光导模

研究一个芯子层是左手材料,其他三层由传统材料构成的四层平板光波导系统,利用图解法对各种TE偏振的导波模式的解进行详细分析.研究表明,四层左手材料光波导既能支持振荡导模,也能支持表面导模,与三层左手材料光波导相比较,此四层波导的导波模式呈现一些新的特性.对于中间传统材料层存在振荡场的情形:芯子层支持振荡导模的光波导中存在基模,并且高阶振荡导模出现模式缺失的性质;芯子层支持表面导模的光波导可以支持基模和多个高阶模式,并且存在模式兼并的性质.对于中间传统材料层存在衰减场的情形,此四层波导结构可等效为三层左手材料光波导.这些新的光波导传输性质对各种光波导器件的制作有潜在的应用价值.