BPM-FSRM混合法分析SOI脊形波导与光纤耦合

用束传播-自由空间辐射模（BPM-FSRM）混合法计算了SOI脊形波导和光纤耦合时的透射率, 提出计算反射率的积分公式. 将该混合法和一般FSRM、菲涅尔公式-重叠积分法的计算结果相比较, 提出只有在弱导条件下, 传统的菲涅尔公式法和重叠积分法才可以同时使用.     

Resonant reflection of a surface acoustic wave from strip waveguides

A numerical study is performed of the oblique reflection of a surface acoustic wave from a strip of finite width deposited on the surface of a half-infinite substrate. The finite element method is used. If the strip–substrate contact supports waveguide modes with the velocity exceeding the surface wave velocity on the free surface of the substrate, then an interval of angles of incidence exists where the surface wave efficiently excites a waveguide mode. The excitation of the waveguide mode is accompanied by a singular behavior of the reflection and the transmission coefficients. The dependence of the magnitude and the phase of the coefficients on the angle of incidence, the frequency, the width and the thickness of the strip is examined. In particular, it is found that the magnitude of the reflection coefficient abruptly almost vanishes and abruptly increases almost to unity within the resonance interval of angles of incidence.     

周期变截面波导中的多缺陷态*

设计了一种具有对称结构的多缺陷周期变截面波导,并在其Bragg禁带中实现了多缺陷态的产生。研究表明,通过调整缺陷的个数和长度可实现对缺陷态数目的选择和缺陷态中心频率的调谐。另外,改变重复周期个数可对缺陷态的带宽进行调节。通过对各缺陷态的声场分布进一步分析,我们发现声压沿波导中心轴呈对称或反对称分布。对称缺陷态的最大声能量总是向长度较小的缺陷处偏移,而反对称缺陷态则相反,总是向长度较大的缺陷处偏移。利用这种偏移特性可实现对多缺陷态的声场调控。这不仅使我们对声缺陷态的认识更加深入,更有利于功能型声波导器件的发展与应用。     

Dispersion characteristics of complex refractive-index planar slab optical waveguide by using finite element method

In this paper, finite element method (FEM) mode analyses of planar slab optical waveguide having complicated refractive index profile are presented. We try to estimate the dispersion graph, mode cut-off condition, group delay and waveguide dispersion for the case of α-power and chirped-type refractive index profile. In order to obtain the more accurate result, we have derived the higher-order polynomial, which establishes the suitable relationship between b and V for different profile of optical waveguide. On the basis of the derived polynomials, the waveguide dispersion is analyzed for different type of refractive index profile waveguide. Our study shows that the waveguide dispersion can be substantially reduced when we deployed the optical waveguide having linearly chirped-type refractive index profile. Earlier too, the arbitrary refractive index profile has been analyzed but to the best of our knowledge chirped-type refractive index profile has not been analyzed till date for the case of planar slab optical waveguide.     

全息波导显示系统中输出光栅的优化

全息波导显示系统中输出光栅的衍射效率、位置和长度对整个显示系统的光强输出均匀性及能量利用率有重要的影响.通常输出光强均匀性由输出光栅的衍射效率决定,能量利用率受多重光栅的位置和长度影响.本文以中心视场光束的输出光强均匀为目的,对相应输出光栅衍射效率的位置分布进行优化与曲线拟合,得到输出光栅衍射效率随输出位置连续递增的分布曲线,并应用到所有视场光束.计算结果表明,相比于传统阶梯状衍射效率分布输出光栅,全息波导显示系统中采用具有连续衍射效率分布输出光栅时的光强输出均匀性得到明显提升.针对部分衍射光束未能进入出瞳的现象,提出错位优化法,按照出瞳大小和使用距离优化各重输出光栅的位置和尺寸,减小了光栅的无效衍射区域,提高了出瞳范围内的能量利用率.     

Ultra-high transmission of photonic nanojet induced modes in chains of core–shell microcylinders

The ultra-high transmission of photonic nanojet induced modes in chains of core–shell microcylinders illuminated by a plane wave is reported. Using high resolution finite-difference time-domain simulation, the periodical focusing of lightwave in straight chains of touching core–shell microcylinders is characterized with the periodicity of photonic nanojets corresponding to the diameter of two microcylinders. The core–shell microcylinders are efficiently coupled to the collimated incident lightwaves. We observe the lightwave with high optical transport of 3 dB in the maxima of transmission spectra for a chain of core–shell microcylinders. The chains of core–shell microcylinders can be assembled inside hollow waveguide and used in a variety of microscopy techniques, biomedical applications, and optical microprobes with subwavelength spatial resolution.     

Use of Anisotropic Materials as Chemical Detectors

Abstract

The visual detection between crossed polarizers, of organic vapors on various liquid crystal films is reported. Non-selective detection is achieved in the ppm range. However, opportunities exist for bettering selectivity and sensitivity as illustrated with a combined polymer-liquid crystal detection system for amines. Also described is the detection of liquid droplets by utilizing changes in the birefringence of polycarbonate membrane filters.     

Refractive index profiles of ion implanted waveguides in thulium sodium yttrium tungstate

Planar waveguides were first formed in thulium sodium yttrium tungstate (Tm:NaY(WO₄)₂) crystals by the implantation of MeV He, P and Ni ions with certain doses at room temperature, respectively. The refractive index profiles of the three ion implanted waveguides were found different to some extent. The present data show that He⁺ ion implanted waveguides in Tm:NaY(WO₄)₂ should be the typical barrier type one, while a combination of radiation damage and radiation enhanced diffusion may be responsible for the refractive index profiles of the MeV Ni⁺ and P⁺ ion implanted waveguides in Tm:NaY(WO₄)₂.     

声矢量传感器线阵波导不变量被动测距研究

介绍一种利用水声信道的统计不变特征(波导不变量)实现被动测距的方法。对接收LOFAR(Low FrequencyAnalysis Record)图使用HOUGH变换等边缘提取技术提取条纹,得到波导不变量以及抛物线参数的估计值,进而得到目标的CPA(Closest Point of Approach)点距离。矢量水听器的振速通道数据所得LOFAR图信噪比明显高于声压LOFAR图,可以提高测距精度。仿真和试验数据结果显示本方法能以较高的精度提取CPA点距离。对比波导不变量经验值和在线估计值所得最近点距离结果,发现使用具有一定精度的在线估计波导不变量值可以显著提高测距精度。