Theoretical model of a planar integrated refractive index sensor based on surface plasmon-polariton excitation

A theoretical model of a new integrated planar surface plasmon-polariton (SPP) refractive index sensor is presented and comprehensively investigated. The main principle of operation of this device is based on high efficiency energy transfer between a p-polarized guided mode propagating in a waveguide layer of the structure and the SPP propagating in the opposite direction in a metal layer separated from the waveguide layer by a dielectric buffer. The high efficiency energy transfer is realised by means of a properly designed Bragg grating imprinted in the waveguide layer. This device is compact, free from any moving parts and can easily be integrated into any planar scheme. Our simulations for the sensor operating at the well developed and commercialised telecom wavelengths are based on coupled mode theory.     

Numerical analysis of plasmon polarition refractive index fiber sensors with hollow core and a long period grating

The main principle of this design is based on the efficient energy transfer between the waveguide mode (WM) and the co-directional SPP provided by a properly designed fiber long period grating (LPG). This LPG is imprinted into a waveguide fiber layer of a specially designed hollow core optical fiber. The simulations are based on the finite element method (FEM) algorithm in electromagnetics and coupled mode theory for gratings. Compared to the previous proposed structure using a fiber Bragg grating (FBG), this novel kind of sensor can greatly enhance the refractive index sensitivity, e.g., from 5.93 nm/RIU (with FBG) to 817 nm/RIU (with LPG) at the sensing refractive index of 1.40. The other advantage is that the working conditions can be performed for the well-developed telecom wavelength windows 1500-1600 nm.     

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     

金属异质波导阵列中的表面等离激元传播特性

提出了一种新的一维金属异质波导阵列的设计方案,即波导芯区周期调制的金属波导阵列.数值模拟的结果表明,金属波导芯区的周期调制引起波导中传播的表面等离激元有效折射率的周期调制,从而可在特定的波段打开一个表面等离激元带隙(如1550nm附近).通过引入合适的缺陷波导单元,可获得特定波长的高品质因子(Q=556)的表面电磁模共振.这一结果可用于设计亚波长的布拉格反射器、光发射器、滤波器等,有可能被用于未来的集成光路.     

Long period grating in/on planar and channel waveguides: A theory description

A comprehensive, complete theory suitable for a long period grating (LPG) on/in a planar or channel waveguide is described on the basis of coupled mode theory. The theory aims at key characteristic parameters with respect to the effect of the LPG, including resonance wavelength, transmission power of the guided mode in the waveguide, full-width at half-maximum (FWHM) of the power attenuation band in transmission spectrum of the guided mode, and coupling coefficient between a guided and a coupled mode. The type of the grating including relief and index modulation, different polarization state combinations of the guided mode and the resonant mode, and slanted grating structure are considered in this theory. The influences of the coupling between two guided modes and between a guided mode and a substrate mode are discussed. The role of cladding layer in a long period waveguide grating is demonstrated in particular. Finally, the expressions for the sensitivity of resonance wavelength as a function of external temperature, pressure and surrounding refractive index are derived.     

Planar anisotropic Mikaelian lens on the basis of EBG-structure

The problem on the synthesis of a planar Mikaelian lens in the form of layered metal?dielectric waveguide with a nonuniform anisotropic dielectric layer is solved. The problem is reduced to solution of the dispersion equations for E and H modes of a homogeneous layered waveguide. As an example of implementation of the solution obtained, the synthesis and analysis of the Mikaelian lens is carried out on the basis of the EBG structure in the form of a planar corrugated open and closed layered metal?dielectric waveguide. For a special case of the closed waveguide, the solution of the problem of synthesis for both polarizations is obtained explicitly.     

Electrically controlled waveguide mode in LC layer for fiber optic applications

A new electrically controlled waveguide mode for optical beams propagating in the plane of a liquid crystal (LC) layer is described. The mode is based on the total internal reflection of light beams from two parallel boundaries, which separates the regions of a liquid crystal cell with different director orientations and refractive indices. In experiments electric field was applied to the initially planar layer to produce the channel with a homeotropic orientation surrounded by the planar regions. It results in focusing and waveguide propagation of a light beam emitted by an optical fiber inserted in a liquid crystal cell. Scattering of light by thermal LC director fluctuations is used to visualize light beams propagation. The obtained waveguide mode can be used for an elaboration of electrically controlled LC switches with low operating voltages. The prototype of such device made with usage of a photolithography and a photo alignment technique is described. The possible ways of optimization of LC-switch are considered.     

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.     

Disposable and compact integrated plasmonic sensor using a long-period grating

This Letter theoretically proposes and investigates an integrated plasmonic sensor that is based on a grating-assisted coupling between a surface plasmon polariton (SPP) and a dielectric waveguide (DW) mode. It consists of a glass slide with a gold film for the propagation of an SPP and a separate DW with a long-period grating. For sensing, the two parts are temporarily combined. After sensing, the former is replaceable, and so the sensor has disposability. The design procedure and analysis method for the sensor are explained. The designed sensor is shown to be very compact. Its characteristics of sensing a change of the refractive index of liquid are analyzed and discussed.     

A magnetically tunable non-Bragg defect mode in a corrugated waveguide filled with liquid crystals

A magnetically tunable, non-Bragg defect mode (NBDM) was created in the terahertz frequency range by inserting a defect in the middle of a periodically corrugated waveguide filled with liquid crystals (LCs). In the periodic waveguide, non-Bragg gaps beyond the Bragg ones, which appear in the transmission spectra, are created by different transverse mode resonances. The transmission spectra of the waveguide containing a defect showed that a defect mode was present inside the non-Bragg gap. The NBDM has quite different features compared to the Bragg defect mode, which includes more complex, high-order guided wave modes. In our study, we filled the corrugated waveguide with LCs to realize the tunability of the NBDM. The simulated results showed that the NBDM in a corrugated waveguide filled with LCs can be used in filters, sensors, switches, and other terahertz integrated devices.     

Theory of absorption integrated optical sensor of gaseous materials

The eigen and noneigen (leaky) modes of a three-layer planar integrated optical waveguide are described. The dispersion relation of a three-layer planar waveguide and other dependences are derived, and the cutoff conditions are analyzed. The diagram of propagation constants of the guided and radiation modes of an irregular asymmetric three-layer waveguide and the dependence of the electric field amplitudes of radiation modes of substrate on vertical coordinate in a tantalum integrated optical waveguide are presented. The operating principles of an absorption integrated optical waveguide sensor are investigated. The dependences of sensitivity of an integrated optical waveguide sensor on the sensory cell length, the coupling efficiency of the laser radiation into the waveguide, the absorption cross-section of the studied material, and the level of additive statistical noise are investigated. Some of the prospective areas of application of integrated-optical waveguide sensors are outlined.     

Theory and practice of long-period gratings: when a loss becomes a gain

Losses of cladding modes are part of the mechanism of operation of a long-period grating (LPG) when it is used as an optical filter. We present a LPG computer simulation that accounts for these losses. On the basis of this simulation, we show that losses result in qualitatively different LPG spectral behavior. There is an optimal loss value that provides sidelobe-free, 100% power transfer from the core to the cladding mode for a uniform LPG. We obtained a simple equation that relates this optimum lose value to the LPG length and the cross-coupling coefficient. Based on the results, we propose new approaches to LPG design in a fiber as well as in waveguide platforms for fiber-optic communication and sensor applications. A design of a LPG reconfigurable filter is suggested.     

Ultralow-bending-loss surface-plasmon-polariton waveguides

We report the transmission, reflection and loss properties of 90-degree and 135-degree bent silicon waveguide and 90-degree and 135-degree bent surface-plasmon polariton (SPP) waveguides composed of metal thin film and silicon. Finite difference time domain simulation analysis shows that the maximum bending transmittances of 90-degree bent and 135-degree bent silicon waveguides are 51% and smaller than 10%, respectively, and the maximum bending transmittances of 90-degree bent and 135-degree bent SPP waveguides are 80% or so, and they are higher 30% and 70% than that of identically-bent silicon waveguides, respectively. Moreover, the SPP waveguide bend with metal thin film as inner layer of the bend and silicon as outer layer of the bend has much higher transmission than ones with silicon as the inner layer and metal thin film as the outer layer. The waveguide bend with metal as the inner layer and dielectric as the outer layer will be potential for integrated photonic devices and subsystem.     

Design of Planar Optic Sensors for Hydrocarbon Detection

A realistic design of evanescent field optical sensors, constituted by three different kinds of planar waveguides covered by a sensing polymeric overlay, is performed. More precisely, the slab, the embedded strip and the ridge waveguides are considered. The sensor operation is simulated, in both the cases of lossy guided and leaky mode propagation, via a home made computer code. The optimal waveguide transverse section and length are identified, the advantages and drawbacks are shown. The ridge waveguide sensor exhibits appreciable characteristics: for a concentration C _w = 200 ppm of toluene in water, the absorbance pertaining to a device L = 2.6 cm long and for the guided quasi-TE₀₀ mode is A ≅ 5, while it is A ≅ 0.054 for a device long L ≅ 24.1 μm and the leaky quasi-TE₁₀ mode. The simulation results suggest that a selective excitation of the suitable propagation mode can enhance the sensor performance.     

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     

平面光波导光场分布的有限时域差分法计算

用有限时域差分法计算了简单三层对称平面光波导中的光场,得到了任意截面上光场的分布.这一方法的优点在于它能完全模拟波导中光场的时域特性,使波导中的光传播完全可视化,模拟横向传播,提取光在波导中的传输模式,也可用于有源波导的计算如光波导放大器.有限时域差分法直接求解依赖时间的麦克斯韦旋度方程,利用二阶精度的中心差分近似,把旋度方程中的微分符直接转换为差分形式.每一步计算都无须作矩阵求逆运算,因此,比其他数值计算方法更有效、精度更高.     

Enhancement of electroluminescence through a two-dimensional corrugated metal film by grating-induced surface-plasmon cross coupling

We report enhancement of electroluminescence through opaque-topped metal cathodes in organic light-emitting devices (OLEDs), which are periodically corrugated in two dimensions. The enhancement is caused by grating-induced cross coupling and outcoupling of surface plasmons. The emission intensity observed at normal direction is enhanced by a factor of 4 compared with that of OLEDs with one-dimensionally corrugated metal cathodes and is higher than that observed from the transparent substrate side in uncorrugated OLEDs. We attribute the enhancement to the fact that the surface plasmons propagating in all lateral directions are coupled out into free space by the two-dimensional corrugated structure of the OLEDs. In addition, the emission from the transparent substrate side is also much enhanced owing to the efficient coupling out of the waveguide modes trapped in the emissive layer.     

基于双面金属包覆光波导的传感器温度特性研究及实验验证

双面金属包覆波导结构(SMCW)是由一层介质波导层被两层金属膜层上下包覆的一种新型波导结构; 本文基于金属层和介质层材料的热-光效应和热膨胀作用, 研究了双面金属包覆波导结构的温度特性. 计算分析的结果表明, 金属膜层的厚度、金属的介电系数、波导层的厚度及其介电常数几乎都与温度变化成比例, 同时, 对双面金属包覆波导结构的波导功能起主要影响的是介质层的厚度值随温度的变化. 本文分别在光谱模式和角度模式下研究双面金属包覆波导结构的反射特性, 并将其应用于基于双面金属包覆波导结构的传感器, 其灵敏度约为21.89 pm/K(光谱模式)和1.449×10^-3 rad/K(角度模式). 最后, 本文对角度模式的模拟分析进行了实验验证, 实验验证结果与模拟分析结果基本一致, 实验所用SMCW样品的平均灵敏度约为0.517×10^-3 rad/K, 与模拟分析的灵敏度结果同一量级. 双面金属包覆波导结构的传感器对温度非常敏感, 且该结构的物理构造简单, 成本低, 具有非常大的潜在应用价值.     

Guided modes in a rectangular waveguide filled with single-negative materials

Based on classical electromagnetic theory, characteristics of guided modes in a rectangular waveguide filled with a pair of single-negative layers are studied. The results show that only surface waves of TE mode can propagate in this peculiar waveguide, no TM mode in any forms can propagate in it. In addition, TE waveguide modes will be affected by permeability ratio μ₁/μ₂ and dielectric layer thickness ratio P. Finally, from the electric field distribution of TE mode, we find the amplitude and location of the electric field can be adjusted by changing the thickness ratio P.     

Sensitivity enhancement in TE mode nonlinear planar optical waveguide sensor with metamaterial layer

The dispersion equation of the TE mode nonlinear planar optical waveguide with metamaterial layer was derived, and the sensitivity of the waveguide sensor was analyzed. The influences of structural parameters on the sensitivity of the waveguide sensor were investigated. We verify that the waveguide sensor with metamaterial layer can dramatically enhance the sensitivity compared with other waveguide sensors.