Propagation properties of a modified surface plasmonic waveguide with an arc slot

We introduce a modified surface plasmonic waveguide with an arc slot. The dependences of distribution of energy flux density, effective index, propagation length and mode area of the symmetric mode supported by this waveguide on geometrical parameters and working wavelength are analysed by using the finite-difference frequency-domain (FDFD) method. Results show that the energy flux density distributes mainly in four corners which are formed by two arcs, and the closer to the corners it is, the stronger the energy flux density will be. The effective index, the propagation length and the mode area are influenced by geometrical parameters, including the width, the thickness and the arc radius of the surface plasmonic waveguide, as well as the working wavelength. It has been shown that the surface plasmonic waveguide with an arc slot has better propagation properties than the surface plasmonic waveguide with a straight slot. This work may be helpful for applying the slot surface plasmonic waveguide to integrated photonics.     

Strongly enhanced mode selection in a thin dielectric-coated layered microcavity laser

Strong mode selection through an enhanced interferential coupling effect was observed in a thin dielectric-coated layered cylindrical microcavity laser. The strong coupling effect was induced owing to an enhanced reflectivity of around 50% at the dielectric-coated inner boundary of a fused silica capillary filled with a dye-doped liquid. At an optimized coating thickness of about 0.4 microm, the lasing peaks appeared only at the wavelengths corresponding to the constructive interference condition, whereas those from a bare capillary were weakly modulated.     

Radiation pattern of an end-fire optical waveguide coupler

A section of an optical waveguide having thickness less than the mode cutoff value adjoining a section having thickness greater than this value serves as an input-output optical waveguide coupler. Expressions for the radiation pattern of this coupler, the angle at which the maximum occurs, and the angular beam width are derived. Calculations of these quantities as a function of coupler thickness for several waveguide-substrate structures applicable at λ = 10.6 μm are presented. Radiation patterns with small angular widths that result in high coupler efficiencies are found to occur when the waveguide and substrate refractive indices are nearly equal.     

Numerical model of the polymer electro-optic waveguide

A numerical design model is presented for the polymer waveguide in an electro-optic modulator. The effective index method is used to analyze the height of the core waveguide and rib waveguide, an improved Marcatili method is presented to design the rib waveguide width in order to keep the strong single mode operation and have a good match with the standard fiber. Also, the thickness of the upper cladding layer is discussed through calculating the effective index of the multilayer planar waveguide structure has been obtained by setting the optical loss due to the metallic absorption to an acceptable value (<0.1 dB/cm). As a consequence, we take the EO polymer waveguide structure of UV15:CLD/APC:UFC170 as an example, an optimized design is reported.     

Central distance of interferential mode patterns of elliptical cora two-mode fiber

By means of the weakly guiding approximation, the mode spot sizes Wx and Wy of the fundamental mode along the semimajor (x-direction) and semiminor (y-direction) axes of the fiber core in elliptical core twomode fiber are discussed. The variation of their ratio value Wx/Wy with the operation wavelength λ and the length ratio a/b between the semimajor axis and the semiminor axis of the fiber core is analyzed. Based onthis analysis, the distribution figures of two-lobe interferential mode patterns are evaluated and simulated quantitatively for different phase difference changes between LPo1 and LPeven11 modes. The two-lobeinterferential mode patterns have the same profile and distribute symmetrically when the phase differenceequals π/2. Their central distance S becomes larger when WX/Wy augments gradually. Furthermore,the equation about the central distance S of the two-lobe interferential mode patterns is given when the operation wavelength varies between 0.65 and 1.31 μm, which is important to applications shuch as sensors and coupling devices between different fibers.     

Parameter optimization and structural design of polymer arrayed waveguide grating multiplexer

First some important parameters are optimized for the structural design of a polymer arrayed waveguide grating (AWG) multiplexer around the central wavelength of 1.55 μm with the wavelength spacing of 1.6 nm. These parameters include the thickness and width of the guide core, mode effective refractive indices and group refractive index, diffraction order, pitch of adjacent waveguides, length difference of adjacent arrayed waveguides, focal length of slab waveguides, free spectral range (FSR), the number of input/output (I/O) channels, and that of arrayed waveguides. Then the bent angles, radii and lengths of all the input/output channels and arrayed waveguides are determined. Finally, a schematic waveguide layout of this device is presented, which contains 2 slabs, 11 input channels, 11 output channels, and 91 arrayed waveguides.     

L波段大功率全带宽波导盒型窗

 由于鬼模振荡的存在,普通波导盒型窗很难获得宽频带输出,其相对带宽一般只有20%～30%。提出一种新的适用于大功率螺旋线行波管非对称全带宽波导盒型窗设计思路,通过３维电磁仿真设计与优化,获得了L波段相对带宽达41.4%盒型窗结构设计参数,且频带内无鬼模振荡,考虑匹配过渡段后整个盒型窗驻波系数模拟计算小于1.1。采用此功率输出结构研制的S波段大功率行波管连续波输出功率达3 kW以上,整管实测驻波系数小于1.6。     

Antenna measurements on the radiator component of an X-band Vlasov-type mode converter

This paper addresses the radiation patterns launched from circular waveguide radiators as the first step in the design of a Vlasov-type mode convertor that will function at high power levels in the X-band frequency range (8 to 12 GHz). The radiating ends of the radiators are each cut at a specific angle relative to the center axis of the waveguide to form the waveguide launcher component of a Vlasov-type mode convertor. The far-field radiation patterns for three radiators were measured with an antenna pattern-mapping system.ATTN: SLCHD-NW-RS     

电磁波在负折射材料填充的3层平板波导中的传播特性

从电磁场理论出发对负折射材料填充的3层平板波导的传播特性进行研究,并进行了数值计算,分析TE和TM波在平板中传播的性质,得到了电磁波的模式方程,与电磁波在右手材料填充的平板波导中的传播特性做了对比,考察了TE模式的能流密度,进行了归一化计算。结果分析表明：基模、一阶模不存在,且任何模式都存在一个截止厚度,随着厚度的增大,模式数量也增多;在一定的入射频率下,平板薄膜厚度趋向一定数值时,可以同时传播多种模式的波,并且入射波频率越高,波导同时存在多种模式的可能性越大;与右手材料相比,左手材料填充相同尺寸的3层平板波导可以传播更高能量的电磁波,导波效果更好。     

Heterostructure with extended optical waveguide for diode lasers

The thickness and composition of diode heterolaser layers are optimized with respect to the ratio of the optical beam width d to the optical confinement factor Γ. The stability of the vertical near field distribution and the most important waveguide parameters to static changes and dynamic variations of the refractive indices of heterostructure layers is tested in the laser operation mode.     

Multimode interference effect in plasmonic subwavelength waveguides and an ultra-compact power splitter

The real part of the effective index is enhanced in a metal-insulator-metal (MIM) surface plasmon waveguide when the thickness of the insulator is quite small and this mechanism can be utilized to achieve some ultra-compact photonic devices. The mode properties of an index-guided multimode plasmonic waveguide of subwavelength size are analyzed and the multimode interference (MMI) effect is investigated. A novel ultra-compact MMI power splitter, with the transverse size less than 1/3 of the free space wavelength, is proposed.     

Simulation and optimization of a polymer directional coupler electro-optic switch with push-pull electrodes

Structural model and design technique are proposed for a polymer directional coupler electro-optic switch with rib waveguides and push-pull electrodes, of which the electric field distribution is analyzed by the conformal transforming method and image method. In order to get the minimum mode loss and the minimum switching voltage, the parameters of the waveguide and electrode are optimized, such as the core with, core thickness, buffer layer between the core and the electrode, coupling gap between the waveguides, electrode thickness, electrode width and electrode gap. Switching Characteristics are analyzed, which include the output power, insertion loss, and crosstalk. To realize normal switching function, the fabrication error, spectrum shift, and coupling loss between a single mode fiber (SMF) and the waveguide are discussed. Simulation results show that the coupling length is 3082 μm, push-pull switching voltage is 2.14 V, insertion loss is less than 1.17 dB, and crosstalk is less than −30 dB for the designed device.     

Acoustical scattering by arrays of cylinders in waveguides

Multiple scattering of acoustic waves in a planar horizontal waveguide by finite-length cylinders is considered. Cylinder height equals the waveguide depth, and both are vertically constrained by the pressure-release boundaries. An analytically exact solution is obtained via normal mode expansion method in conjunction with the concept of the T matrix. The problem is decomposed into an infinite number of two-dimensional multiple scattering problems, modulated by waveguide mode shapes. Examples are presented for an isovelocity waveguide in which the medium is uniform and the waveguide depth is constant. It is found that, in numerical computations, including one or two evanescent modes captures the essence of the evanescent modes. Multiple scattering in the waveguide is compared with the corresponding two-dimensional case. It is concluded that, in low frequencies, the wave patterns in the two cases are very similar, with a shift in the frequency. The similarity diminishes when there are multiple propagating modes. Despite the mode mixing, some key features in the scattering as observed in the two-dimensional problem remain observable in the waveguide case.     

TE0导模干涉刻写周期可调亚波长光栅理论研究

通过棱镜耦合激发非对称金属包覆介质波导结构中的TE₀导波模式, 利用两束TE₀模的干涉从理论上实现了周期可调的亚波长光栅刻写. 分析了TE₀模式的色散关系, 刻写亚波长光栅的周期与激发光源、棱镜折射率、光刻胶薄膜厚度及折射率之间的关系. 用有限元方法数值模拟了金属薄膜、光刻胶薄膜和空气多层结构中TE₀导模的干涉场分布. 研究发现, 激发光源波长越短, TE₀ 模干涉刻写的亚波长光栅周期越小; 光刻胶越厚, 刻写的亚波长光栅周期越小; 高折射率光刻胶有利于更小周期亚波长光栅的刻写. 相较于表面等离子体干涉光刻, 基于TE₀ 模的干涉可在厚光刻胶条件下通过改变激发光源、棱镜折射率、光刻胶材料折射率、特别是光刻胶薄膜的厚度等多种方式实现对亚波长光栅周期的有效调控.     

Field Patterns of the TE Modes in Ridge-Trough Waveguide

A single-ridge waveguide with a symmetrical longitudinal trough, designated as a ridge-trough waveguide has been used as a transition in a V-band (50-75 GHz) wafer probe recently. In this paper, the field patterns for the dominant TE mode and the first higher TE mode in ridge-trough waveguide with different configurations are presented by finite element method. The field patterns in this paper have important values for us to understand the transmission characteristics of ridge-trough waveguide, and will be of practical significance in designing ridge-trough waveguide components in microwave and millimeter wave engineering.     

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.     

涂覆双层石墨烯的介质纳米线表面等离子体光波导的模式特性研究

设计了一种由涂覆双层石墨烯的圆形介质纳米线组成的表面等离子体光波导。利用有限元法(FEM),数值分析了纳米线半径、介质夹层厚度、石墨烯化学势以及工作频率对波导所支持的电磁场模式的有效折射率、传播长度、归一化模式面积以及品质因数等模式特性的影响。结果表明,这种新型的混合表面等离子体光波导具有很强的模式束缚能力,归一化模式面积非常小,可以实现极高密度的器件集成,并且传输损耗较低。     

Mode Content Determination in a Multimode Waveguide from Radiation Pattern Measurements Using the Genetic Algorithm

This paper presents a novel technique for determining the mode content in a multimode waveguide from the radiation pattern measurements. The technique employs the Genetic Algorithm (GA) for determining the mode content in the waveguide from the measured pattern and a numerical method for simulating radiation patterns for the modes propagating in the waveguide. By numerical experiments, we validate the feasibility and effectiveness of the proposed technique, and illustrate its sensitivity to the number of observation points and random noise in the measurement.     

E面和H面方向图等化的双模圆锥喇叭设计

 介绍用于Φ7.3 m Cassegrain天线的高功率馈源喇叭的设计。为使E面和H面方向图在照射区域内具有高的等化度，选择双模圆锥喇叭作为馈源的结构形式。由于高功率源采用BJ-32波导输出信号，故馈源系统中还应包含一个矩形到圆形的模式转换器，将TE10模转换为TE11模。设计了双模圆锥喇叭和模式转换器，并进行了功率容量估算。测试结果表明，所设计的馈源达到了设计要求，理论计算结果和实验测试数据吻合良好。