对称单负介质包层平面波导的模式特征

系统研究了负μ材料(MNG)作为包层的对称三层平板波导的传输特性. 研究发现,这种波导既支持快波的传播,又支持TE₀,TE₁模式的慢波传输. 其模式特性不同于左手介质波导和传统介质波导,导模存在的模折射率范围要比它们的大. MNG波导的TE₀快波模缺失,且TE_m模(m>1)的传播常数大于TM_m模的传播常数. TE_m模具有双模特征,且与波导的结构参数密切相关,导致波导中的净能流出现负值. 关键词： 单负介质 平板波导 快波与慢波 传播常数     

The properties of two-dimensional photonic crystals bandgap structure with rhombus lattice

The relative bandgap ω_R of photonic crystals structure with rhombus lattice for both TE and TM modes is studied by the plane wave expansion method. Based on the analysis, a bending waveguide of U type can be easily obtained. The steady-state distribution of the electric field with ω = 0.4765(a/λ) of TM mode is given by FDTD method and the transmission is obtained by FFT of the time domain field. All of the sufficient analysis shows the conceptual framework of the proposed rhombus lattice PCs and its great potential application in photonic integration circuit.     

锆钛酸铅双层膜的铁电及光学特性研究

采用化学溶液沉积法在LaNiO₃涂布的硅晶片上制备了高度(100)择优取向,表面均匀、平整、致密无裂纹的PbZr_0.5Ti_0.5O₃/PbZr_0.4Ti_0.6O₃双层膜. 双层膜具有单一的钙钛矿相,同时拥有良好的铁电性能,剩余极化强度高达64μC/cm²,平均矫顽场仅为43.6kV/cm. 棱镜-薄膜耦合实验结果表明PbZr_{关键词： 铁电薄膜 平板光波导 锆钛酸铅 棱镜-薄膜耦合}     

Guided modes in slab waveguides with a left handed material cover or substrate

We study guided modes propagating along a dielectric slab waveguide with a left handed material (LHM) cover or substrate. The dispersion relation is derived by using normalized waveguide parameters. An analytical method is then proposed to calculate the universal dispersion curves. Different from a slab waveguide with a LHM core, we find that guidance properties are strongly dependent on dielectric permittivity ε and magnetic permeability μ of the substrate and cover layers. For oscillating guided modes, fundamental zero order mode is not always absence, sometimes it exists in a restricted range of normalized propagation constant. First order mode behaves as other higher order modes and exists up to infinite high frequency. Higher order modes have no double degeneracy in the case of LHM cover layer. For surface guided modes, the existence and the type of the mode solutions with respect to different parameters are classified systematically and discussed in detail. Unlike a slab waveguide with a LHM core where the dispersion curve of TE₁ surface mode continues with that of oscillating TE₁ mode, the dispersion curve of TE₁ surface mode continues with that of oscillating TE₀ mode. It seems that the two different kinds of modes compensate each other to form one whole mode. Both TE and TM guided modes are discussed.     

The fabrication of polymer-based evanescent optical waveguide for biosensing

A polymer waveguide was fabricated to amplify the evanescent optical field for biosensing. The structure of waveguide was designed to propagate a normal single mode at the input and output regions for low loss beam coupling and propagation. A sensing region was formed in the middle of the waveguide to activate the evanescent mode and to induce high birefringence by depositing a thin dielectric film with a high refractive index on a single mode waveguide. A polymer waveguide with the dimensions of 7 μm-width and 2.5 μm-thickness was fabricated by photolithography and dry-etching. The active region of the TiO₂ thin film was fabricated with the dimensions of 20 mm-length, 20 nm-thickness and 2 mm-tapered tail. A polarimetric interference technique was used to evaluate the evanescent waveguide biosensor, and biomaterial such as glycerol was tested. The sensitivity of the sensor increased with increasing TiO₂ film thickness. For the fabricated waveguide with a 20 nm-thick TiO₂ film, the measured index change to the lead phase variation of 2π was 1.8 × 10⁻⁴.     

A partially reflecting metal cladding: its effect on the modes of dielectric optical waveguides

If the metal cladding of a dielectric optical waveguide is sufficiently thin to be only partially reflecting, then the waveguide modes differ from those of the conventional metal-clad waveguide. The TE modes are little affected by a variation in the metal thickness but the TM modes change considerably due to a coupling between the waveguide modes and the surface plasma waves supported by both the metal: dielectric interfaces and the metal film. It is the refractive index of the dielectric cladding which is remote from the guiding core that determines whether the lowest order TM mode is the TM₀ or TM₁ mode. This dielectric cladding also strongly influences the attenuation of the TM modes and, if the guide supports a TM₀ mode, then the attenuation of the TM modes far from cut-off are an order of magnitude higher than that of the corresponding modes when the guide cannot support a TM₀ mode. If the guide can support a TM₀ mode then its dimensions can be chosen such that it will support the TE_N and TM_N modes with equal phase velocities. A lossless approximation is used to develop an expression which will specify the required guide dimensions directly and parametric plots of these dimensions are discussed.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

金属包层对称平面单轴晶体波导的模式场(Ⅱ)

对于晶体光轴平行于波导界面的结构,讨论了光在金属包层对称平面单轴晶体波导(波导层是单轴晶体,两个波导界面均为金属)内的传输特性.解析地得到了这种结构下波导模式场的精确解.模式场的性质因单轴晶体的性质不同而异.对于正单轴晶体,波导的主模是横电波,任何频率的光波均可激励该模式;当频率满足一定条件时,波导内传输单模,否则,将激励起高阶模式.高阶模既非TE波,也非TM波,而是两者耦合而成的混合模.对于负单轴晶体,波导的主模是一种混合模,该模式同样可被任何频率的光波所激励;当频率满足一定条件时,波导内传输单模,否则 关键词： 平面金属波导 单轴晶体 模式场 混合模     

Electromagnetic wave modulation in hollow vanadium dioxide microcrystals

The optical properties of vanadium dioxide (VO₂) single crystals with a hollow rectangular inner channel are numerically simulated. In such microstructures, electromagnetic waves are shown to propagate in the form of waveguide modes, and the semiconductor-metal phase transition in VO₂ results in substantial modulation of the mode propagation constant. The propagation constants are calculated for TE, TM, and EH modes in the spectral range 0.8–1.3 μm.     

圆波导硅探测结构对X波段电磁波模式的响应

采用数值模拟和理论分析方法,研究了圆波导内置n-Si探测结构对X波段几种常用电磁波模式的电场响应。首先基于强电场下的热载流子效应,设计了一种利用n-Si进行高功率脉冲实时测量的圆波导探测结构。接着采用三维并行电磁场时域有限差分方法,模拟研究并分析了TE11(两种极化方向)、TM01和TE01模式作用下圆波导探测结构内的横向电场分布特点。结果表明:不同模式下探测芯片内的横向电场均以径向电场为主,径向和角向电场幅度比约为10,而芯片在圆波导内引入的横向电场驻波比均不大于1.3。最后推导了圆波导探测结构在不同模式电场作用下的灵敏度表达式,理论分析指出了探测结构的最大承受功率与圆波导模式有关,最高可达422MW,响应时间则均为ps量级,初步证实了该探测结构可用于X波段百MW级脉冲波源在线探测的可行性。     

High extinction ratio metal-insulator-semiconductor waveguide surface plasmon polariton polarizer

The attenuation characteristics of a multilayer metal clad GaAs-AlGaAs optical waveguide polarizer are theoretically investigated. The dispersion relations and field distribution of the multilayer structures are calculated for different geometrical parameters and material properties. The polarizer studied consists of a single mode finite/infinite metal clad GaAs-AlGaAs waveguide with a dielectric (SiO₂/Si₃N₄) buffer layer inserted between the metal and the waveguide.Conventionally, the TM polarized waves are found to exhibit an absorption peak at a particular buffer thickness (called critical buffer thickness).We shall show that the maximum TM absorption can be improved by a multiple factor up to 7 by choosing a buffer layer thicker than its critical value. This corresponds to an extinction ratio of 1470 dB for a polarizer length of 1 mm. Further, thicker buffers reduce the insertion losses and values as low as 0.1 dB can be obtained. The strong TM absorption in these structures is interpreted as resonant coupling of the guided mode to the lossy surface plasmon polariton supported by the thin metal film. Thicker buffer also reduces the TE losses (insertion losses) and hence increases the extinction ratio (ratio of TM to TE losses).This can be achieved by optimizing the buffer and the metal thicknesses. Another equally efficient polarizer can be designed by positioning a dielectric (same as buffer) layer (superstrate layer) above the metal film and then optimizing the buffer, metal and the superstrate thicknesses. We also show that the proposed polarizer with the superstrate layer is highly stable even when exposed to the extreme atmospheric changes.     

同轴TEM-矩形TE10模式变换器的优化设计

用ＨＦＳＳ软件和网络理论对Ｓ波段同轴ＴＥＭ－矩形ＴＥ１０模式变换器进行了优化设计。同轴波导工作于过模状态,可同时传输ＴＥＭ、ＴＥ１１、ＴＥ２１模。模式变换器可应用于高功率微波的能量提取系统,优化设计方法可用于通过短路活塞来实现调配的同轴－矩表、圆波导－矩形的模式变换器。     

同轴TEM－余矩形TE10模式变换器的优化设计

 用HFSS软件和网络理论对S波段同轴TEM－矩形TE₁₀模式变换器进行了优化设计。其中同轴波导工作于过模状态,可同时传输TEM、TE₁₁、TE₂₁模。模式变换器可应用于高功率微波的能量提取系统,优化设计方法可用于通过短路活塞来实现调配的同轴－矩形、圆波导－矩形的模式变换器。     

非对称金属包覆左手介质平板波导的微扰分析

基于微扰方法分析非对称金属包覆左手介质平板波导的特性,给出了该波导的复有效折射率的一级近似解,并对波导的传输特性和损耗特性进行了数值模拟.结果表明：非对称金属包覆左手介质平板波导没有零阶模式|TE1模传播系数随波导厚度的增加迅速减小,损耗系数随波导厚度的增加快速增加,达到最大值后又迅速减小|非对称金属包覆左手介质平板波导传输特性相对于左手介质三层平板波导传输特性发生了很大改变,TM1模,TM2和 TE2模式以及更高阶模式在截止厚度附近出现双值现象|特别在二阶及高阶模式中,TE模式相对于TM模式具有高传输低损耗的特性,而以右手介质为芯层的金属包覆波导不具有这一特性.     

X波段高功率微波TE11模圆极化器

 基于圆波导TE₁₁模的模式简并特性和微波在椭圆波导中传输两个正交TE11模式相速不同的性质,研制了一种带有椭圆波导结构的圆波导TE₁₁模圆极化器。该圆极化器通过圆波导到椭圆波导的过渡段,将输入的线极化TE₁₁模式分成两个等幅、正交的TE₁₁模,然后调整椭圆波导长度,使得两个正交的TE₁₁模式的相位差为90°,实现了TE₁₁模式微波线极化到圆极化的转换。利用时域有限差分软件优化设计了该圆极化器,并按照优化的结构尺寸加工了一套实验装置进行了实验测试,测试结果表明：在工作频率9～10 GHz范围内,该圆极化器轴比小于1 dB,驻波比小于1.1,且功率容量大于1.6 GW。     

Semi-analytical analysis of lithium niobate photonic wires

Lithium niobate (LiNbO₃) photonic wires are of growing interest in the field of nonlinear optics and to fabricate micro-ring resonators. In this paper the design and analysis of LiNbO₃ photonic wires by a semi-analytical technique is presented. The two-dimensional refractive index profile of the waveguide is transformed into lateral one-dimensional equivalent-index profile by the effective-index method. A transfer matrix method is then applied to this lateral equivalent-index profile of the waveguide to determine the propagation constants and electric-field distributions of the guided modes. Single mode photonic wires at 1.31 μm transmitting wavelength are designed for both TE and TM polarizations and finally, the matrix method is employed along with the conformal mapping technique to determine the bending loss of the curved photonic wires for different radii of curvature. The process needs less computation power, both in terms of elapsed time and memory, and can also be applicable to other photonic materials.     

Investigation of defect modes in a defective photonic crystal with a semiconductor metamaterial defect

In this work, we theoretically investigate the properties of defect modes in a defective photonic crystal containing a semiconductor metamaterial defect. We consider the structure, (LH)^N/D^P/(LH)^N, where N and P are respectively the stack numbers, L is SiO₂, H is InP, and defect layer D is a semiconductor metamaterial composed of Al-doped ZnO (AZO) and ZnO. It is found that, within the photonic band gap, the number of defect modes (transmission peaks) will decrease as the defect thickness increases, in sharp contrast to the case of using usual dielectric defect. The peak height and position can be changed by the variation in the thickness of defect layer. In the angle-dependent defect mode, its position is shown to be blue-shifted as the angle of incidence increases for both TE and TM waves. The analysis of defect mode provides useful information for the design of tunable transmission filter in semiconductor optoelectronics.     

含左手材料对称三层平板空气波导的模式特性

研究了左手材料作为衬底及覆盖层的对称三层平板空气波导的传输特性.快波和慢波都可以在这种波导中传播.快波不存在基模模式,只有0阶和1阶的TE或TM模才会出现慢波.当左手材料的相对介电常量和相对磁导率相等时,TE、TM模式完全简并,当其相异时简并消除.可以存在同阶模式的双传播模.     

Characterization of laser waveguides in Nd:CNGG crystals formed by low fluence carbon ion implantation

We report on Nd:CNGG active planar waveguides produced by 6.0 MeV carbon ion implantation at fluence from 1 × 10¹⁴ ions/cm² to 8 × 10¹⁴ ions/cm². The refractive index profiles, which were reconstructed according to the measured dark mode spectroscopy, showed that the refractive indices had negative changes in the surface region, forming typical barrier waveguide. The width of waveguide structure induced by carbon ion implantation is ∼3.8 μm. The typical barrier-shaped distribution may be mainly due to the nuclear energy deposition of the incident ions into the substrate. By performing a modal analysis on the observed TE modes, it was found that the TE₀ and TE₁ modes can be well-confined inside the waveguide.     

一种新型慢波结构TM01-TE11模式转换器的数值模拟

 设计了一种新型L波段慢波结构式圆波导TM₀₁-TE₁₁模式转换器，该转换器的尺寸为φ15.0 cm×40.8 cm，通过金属分割片将圆波导分成两个180°区域并在其中一个区域内设置半环形慢波结构。当TM01入射时，在两个区域内激励起扇形波导TE11模式，由于慢波结构的存在，该模式在两个区域内的传播常数不一样。适当调节慢波结构的参数，可使两个区域内传输的扇形TE11模式在金属分割片尾部相位相差180°，这两个扇形TE11模式耦合成为圆波导TE11模式输出，实现模式转换。建立数值模型并进行了模拟，结果表明在工作频率1.8 GHz处转换效率96%，反射率低于0.04，功率容量超过1.7 GW。