基于导模共振效应的多通道窄带滤光片的设计

基于导模共振效应设计了几种多通道窄带滤光片,并利用严格耦合波法分析其光谱特性。在设计的单层滤光片的基础上增加第一层高折射率缓冲层,当厚度为523.8 nm和689.2 nm时,得到双通道和三通道的反射峰,在此基础上增加第二层厚度为768 nm的低折射率缓冲层,得到四通道的反射峰。另外,通过调节单层滤光片的入射角度得到对称的双通道反射峰。     

一种窄带导模共振负滤光片的设计

由于弱调制光栅可以等效为平面波导,本文从平面波导的本征方程出发,导出垂直入射时弱调制光栅共振位置的表达式.分别以单层、双层膜系导模共振光栅结构为例,研究了光栅层厚度、周期、占空比对共振波长的影响.结合光学薄膜理论设计出一种窄带导模共振负滤光片.由于导模共振对入射波参数和光栅参数都极为敏感,具有窄带效应,用来制作窄带负滤波片非常可行.     

单层膜多模导模共振滤光片的电场增强效应研究

本文研究了单层膜多模导模共振滤光片的电场增强效应.单层膜导模共振滤光片同时兼具波导和相位匹配功能的物理机制得到了论证.当光栅厚度不断增加将出现多模共振效应,导致高阶泄漏模电场增强效应的产生.电场增强振幅的最大值反映导模共振滤光片的泄漏程度.通常在同一共振位置处电场增强振幅的最大值越大,其带宽就越小.     

亚波长波导光栅导模共振研究

弱调制介质光栅可等效为平板波导,经其衍射的高级次子波与波导模式耦合时,形成导模 共振。由高级子波在介质光栅中的光程及菲涅耳相移,导出了垂直入射时弱调制介质光栅共振位置的解析表达式,其预测结果和严格耦合波理论所得值一致。导模共振对入射波参数和光栅参数极为敏感,具有窄带效应,可用来制作窄带滤波片。     

磁悬浮列车磁轨耦合内共振分析

磁悬浮列车磁轨耦合共振能使车身剧烈振动,导致车辆平顺性变差。为研究内共振发生条件,建立单点磁轨模型,得到电磁铁和电磁铁电路间机电耦合动力学微分方程。根据多尺度法得到耦合系统频率满足2:1时的内共振幅频方程和内共振一次近似解。数值计算结果表明：电磁铁等效质量、电磁系数、电路总电荷量以及电磁铁线圈等效电阻等参数是影响电磁铁及电量振幅峰值的因素。通过分析磁轨之间的内共振参数特性,得出各参数对磁轨幅值的影响规律和内共振产生条件,可为磁浮列车悬浮系统稳定性设计提供理论计算方法。     

纳米多孔光波导漏模共振传感器的折射率灵敏度分析(英文)

在玻璃基片上射频溅射50 nm厚的金膜,然后利用TiO2胶体溶液在金膜表面制备了厚度约为320 nm的TiO2纳米多孔薄膜.以此双层膜为漏模光波导芯片,构建了基于Kretschmann结构的波长调制型光波导漏模共振(LMR)传感器.利用扫描电子显微镜(SEM)观测了TiO2纳米多孔薄膜的表面和横截面形貌.实验研究了在纳米多孔光波导中给定漏模的共振波长及折射率灵敏度与入射角的依赖关系.结果表明,随着入射角的增大,共振波长逐渐蓝移,折射率灵敏度随之下降.此外,与传统的表面等离子体共振(SPR)传感器进行了对比,结果表明在相同的共振波长下,纳米多孔光波导LMR传感器折射率灵敏度大于SPR传感器.     

局域共振型五模超构材料的低频声波调控方法

五模超构材料是一类具有固体结构与"流体"特性的人工微结构,由于较好的压缩波与剪切波的解耦合能力、 较低的填充率、丰富的晶格构型及可调参数较多等特点,在声波/弹性波隐身衣、声学波导、声学超构表面等声波调控领域具有潜在应用.由单质材料组成的五模超构材料可以被看作是布拉格散射型的声子晶体,其工作频率在高频波段,而目前针对低频...     

平面波与层状多孔介质海底的反射和透射

针对典型的海底介质结构情况,研究了从海水入射到含有非固结沉积层的层状流体饱和多孔介质海底的平面波的反射和透射问题,分析了沉积层和基岩中纵、横波速度和衰减的频散变化特点,在沉积层厚度和频率变化时,对海水-海底界面上的位移势函数反射系数进行了计算和分析。研究结果表明：在沉积层厚度一定的情况下,较高频率时,沉积层对海水中声场的影响较大,而频率较低时,基岩对海水中声场的影响较大。在以不同的掠射角入射时,由于沉积层中质点的法向共振,广义位移势函数反射系数随频厚积的变化曲线会出现一系列的共振峰,随着掠射角的减小,共振峰个数减少,但共振峰的幅度会增加。     

S型圆管弯曲模的设计和制造

用2段相隔一定距离的直线模腔,替代整体加工较为困难和复杂的曲线模腔.完成对产品的加工制造.直线模腔加工便利,并且可以同步、整体加工,制造精度较高.还能根据不同形状的产品尺寸,通过调整模具的垫块高度,以及上、下模各自的2个分离模腔的间距,满足了产品要求,避免重新制造模具.     

导模法生长蓝宝石单晶光纤的缺陷和光学特性研究

通过导模法(EFG)成功生长了蓝宝石单晶光纤(直径400~1000 μm, 长度500 mm)。光纤的横截面大致为圆形, 侧面无明显的小面, 直径变化小于40 μm。本研究对晶体缺陷, 例如微气泡, 包裹物和生长条纹等进行观察与分析, 得出: 大多数微气泡是球状的, 且存在于光纤的外侧缘; 在蓝宝石光纤外侧面也观察到少量的钼包裹物元素; 新模具在前几次使用中往往会产生更多的钼夹杂物, 在多次使用后降低。通过对熔体膜流体流动的实验和数值模拟, 研究蓝宝石光纤中微气泡尺寸和分布, 实验和数值模拟的结果显示出良好的一致性。微气泡的分布取决于熔体膜处的流体流动模式, 流体流动的涡流使微气泡在热毛细对流作用下移动到蓝宝石光纤外侧缘。633 nm处的吸收损耗为9 dB/m, 包裹物和表面不规则性会增加散射损耗。     

Guided-mode resonance filter with an antireflective surface consisting of a buffer layer with refractive index equal to that of the grating

A type of guided-mode resonance filter (GMRF) with an antireflective surface consisting of a buffer layer with refractive index equal to that of the grating is proposed, and the approximate design approach is presented. The relation between the filter linewidth and the coupling loss is used to analyze the filter properties by using different derivation methods. It is shown that the dispersion equation of the slab waveguide may provide a reliable approximation in estimating the resonance locations of the GMRF with an antireflective surface. The buffer layer functions as an intermediate layer between the grating and waveguide layers. This reduces the coupling and out-coupling of a mode of the waveguide, which results in significant reduction of the coupling loss and the filter linewidth with the antireflection condition nearly preserved. By changing the thickness of the buffer layer, different linewidths can be obtained with spectral symmetry and sideband suppression almost kept the same. The slight shift of resonance wavelengths due to the variety of the buffer layer thickness and the etching effects can be adjusted to the design value by changing the grating period. Accurate etch depth control to avoid underetching is necessary. The electric field distributions under resonance conditions shows that the buffer layer increases the mode confinement, thus narrowing the filter linewidth.     

Analysis of the transmission characteristics of an internal reflection microstructure grating

The transmission characteristics of an internal reflection grating primarily integrated into light-emitting diodes are numerically calculated and optimized by using rigorous coupled-wave analysis (RCWA). The obvious polarization effect of the near field distribution is demonstrated. To easily analyze the transmittance performance of the internal reflection grating, simple methods involving scalar diffraction theory and effective medium theory are used. The validity of both methods is quantitatively evaluated by comparing the transmittance results obtained using the simple methods and RCWA. The limitation of both simple methods mainly depends on the grating structure parameters, such as the normalized period and normalized groove depth. Generally, when the dimensions of the normalized period is more than twofold wavelengths of incident light, the scalar treatment can be used to calculate precisely the transmittance of the optical element within 5% error. Also, the validity of the scalar theory is slightly influenced by the change in incident angle. The effective medium theory is accurate for evaluating the transmittance within 1% error when higher-order diffraction waves other than zeroth-order waves do not propagate.     

Light polarization and color from guided-mode resonance filter

The characteristics of reflected light of a 1-D guided-mode resonance filter (GMRF) are studied in this paper. A triple-layer GMRF is designed by using the finite difference time domain method under non-polarized light illumination. Numerical results show that the reflectance spectra of TE and TM polarizations can be changed by altering the fill factor f of the GMRF. Moreover, by calculating the color of the reflected light with the chromaticity theory, we find that the color of reflected light becomes pure when f is 0.9. The results show that the color and polarization degree of the reflected light of a GMRF are tunable by altering the fill factor.     

Design of a nonpolarizing beam splitter based on the form birefringence of a subwavelength grating inside a glass cube

We propose a design concept to design a nonpolarizing beam splitter with a compact sandwich structure that has a subwavelength grating. The design is based on effective-medium theory and rigorous coupled-wave analysis. The simulation shows that a subwavelength grating inside a glass cube can eliminate the polarization effect.     

Parametric optimization of narrow bandstop optical filters using the self-suspended subwavelength grating for TE polarization

Instead of a conventional fixed multilayer grating, a self-suspended subwavelength grating (SSG) which consists of a single grating layer and possesses tunable functions, is investigated by the rigorous coupled-wave method in detail. Through optimizing various parameters including the incident wavelength, the grating period, the grating thickness and the grating filling factor, we demonstrate that the silicon dioxide (SiO₂) SSG owns a narrow reflectance linewidth in the case of TE polarization. For the SiO₂ SSG, the reflectance peak splits into two branches when the incident light deviates from normal incidence. In addition, the reflectance property of the SiO₂ SSG with unoptimized parameters is also presented for comparison, which exhibits a much larger reflectance linewidth. It is expected that the SiO₂ SSG should be used as narrow bandstop optical filters for TE polarization in micro optics systems.     

A resonance method of measuring the reflection and transmission coefficients of a directional coupler

A method of determining the complex reflection and transmission coefficients is considered, based on measurements of the resonance characteristics of a short-circuited waveguide, excited through an inductive iris. The parameters of the coupler in the R2-54/3 type panoramic VSWR measuring instrument are measured. __________ Translated from Izmeritel’naya Tekhnika, No. 3, pp. 60–64, March, 2007.     

光栅衍射特性的耦合波分析、计算与讨论

本文从麦克斯韦方程组及电磁场边界条件出发,推导了广泛应用于各类光栅衍射问题的矢量分析方法--严格的耦合波分析方法.针对光栅的衍射特性,编写了基于严格的耦合波分析方法的计算程序,并以TE模情形为例对光栅的衍射效率和收敛性作了数值计算.结果表明,当谐波数不断增加,即便对于厚光栅(d/λ>10)情形,光栅的衍射效率仍将收敛于某一确定值.     

Design of linear phase FIR notch filters

This paper investigates some approaches for designing one-dimensional linear phase finite-duration impulse-responses (FIR) notch filters, which are based on the modification of several established design techniques of linear phase FIR band-selective filters. Based on extensive design examples and theoretical analysis, formulae have been developed for estimating the length of a linear phase FIR notch filter meeting the given specifications. In addition, the design of two-dimensional linear phase FIR notch filters is briefly considered. Illustrative examples are included. This work was supported in part by a University of California MICRO grant with matching supports from Rockwell International and CES Inc.