Negative-index dispersion and accidental mode degeneracy in an asymmetric spoof-insulator-spoof waveguide

It has been recently demonstrated that negative-index dispersion and mode degeneracy can be achieved by manipulating a spoof-insulator-spoof(SIS) waveguide. In this paper, we propose a new SIS waveguide, which is composed of two spoof surface plasmon polaritons(SSPPs) waveguides drilled with periodic rhomboidal grooves. Both the symmetric and asymmetric cases are investigated. Our simulation results show that the asymmetric SIS waveguides are more significant.By tailoring the tilt of the rhomboidal grooves, the negative-index dispersion can be achieved and the microwave band gap(MBG) can be effectively modulated. At a critical tilt, there appears an accidental mode degeneracy at the edge of the first Brillouin zone. The excitation and propagation of the two coupled modes sustained by the asymmetric SIS waveguides are also demonstrated.     

Optical modes in a plasmonic waveguide with electrically anisotropic metamaterial

We study the optical modes in a plasmonic waveguide with electrically anisotropic metamaterial and dielectric, including symmetric (anti-symmetric) photonic mode and symmetric (anti-symmetric) plasmonic mode. The dispersion curves for these modes are derived, and a graphical method is used to calculate the solution of symmetric photonic mode and anti-symmetric plasmonic mode. By simulation results the conditions of the existence for these modes are deduced in each case.     

Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton(SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding.With Maxwell's equations and Maxwell stress tensor,we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides.The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters.Importantly,an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation.These special optical properties will open the door for potential optomechanical applications,such as optical tweezers and actuators.     

Modulation instability of magnetostatic waves in a magnetically coupled two-layer structure

Modulation instability of direct bulk magnetostatic waves in structures consisting of two magnetically coupled planar films separated by a nonmagnetic layer is studied. It is found that, depending on the type of excitation of the waveguide modes, mode coupling can either change the characteristics of the modulation wave instability or ensure their stability with respect to the corresponding perturbations by affecting the dispersion properties of the structure.     

A Defect Effect to Light Transmission through Acute Bending Coupled Cavity Waveguide in a Two-Dimensional Photonic Crystal

Light propagation through a coupled-defect waveguide with a 63.5° bend in a two-dimensional （2D） photonic crystal is investigated. The waveguide modes are non-degenerate monopole state and dipole defect state of a square lattice for two different branches. To increaze the transmission in the bending waveguide, we propose a method to rotate the localized state by introducing a cavity. The higher coupling efficiency and transmission shift. new type defect with a sheared square rod into coupled in the bending waveguide are obtained with proper shear     

Slow propagation of plasmonic modes in a symmetrical waveguide containing anisotropic metamaterial

We study the slow propagation of plasmonic modes in a three-layer symmetric waveguide with anisotropic metamaterial claddings and a dielectric core. The dispersion equations for symmetric and anti-symmetric plasmonic modes are derived, and a graphic method is used to verify the zero-group-velocity point on the dispersion curves. Simulation results show the influences of signs of tensors and anisotropy of metamaterial on trapped plasmonic modes.     

刻蚀光纤布拉格反射器特性的理论分析

从理论上研究了波导耦合型刻蚀光纤布拉格反射器的特性。采用正交模式耦合理论描述其中的光栅辅助正反向模式耦合，用非正交模式耦合理论描述输入输出接口的模式激发，给出了分析耦合波导布格瓣反射器的角析表达式，分析表明刻光张布拉格反应器中存在三种布拉格反应，在频谱中表现为六个分立的反射峰，与实验结果相符，其反射率不仅决定事系数，还与其结构参数，尤其是Ａｌ２Ｏ３层的厚度，Ａｌ２Ｏ３层与光纤芯的距离以及匹配层折射     

Observation of indirect parallel pumping of magneto-elastic modes in layered YIG/GGG structures

In this work we report new experimental results on nonlinear excitation of magnetoelastic (ME) modes in layered YIG/GGG waveguide structures at GHz frequencies, obtained by a guided-wave light scattering technique. It is shown that the fundamental spin-dipole wave (SDW) mode induces a secondary microwave field at double frequency that can efficiently excite shear elastic modes of the structure. The distinctive feature of a mechanism for ME coupling proposed is that it is free from the selection rules and provides continuous excitation of elastic modes within a wide frequency range by means of the standard microstripe line excitation system.     

单光子晶体界面介质波导中的慢光效应

研究了单光子晶体界面介质波导中的慢光效应.芯层-空气层界面的全内反射效应以及光子晶体基底的禁带效应共同形成了对光场能量的横向约束.用基于超元胞的平面波展开法计算得到了导模色散曲线,并据此对其色散、群速以及群速色散性质做了详尽分析.由于利用了色散曲线慢光区域内拐点附近低群速色散的部分,该单光子晶体界面介质波导具有良好的慢光特性.对两个不同导模计算得到的平均群速分别为c/98和c/376,可用相对频带宽度分别达到2.1×10-3和4.1×10-4.另外,该慢光结构可以侧向耦合的方式克服光子晶体慢光波导耦合困难的缺点.     

Tunable optical switch based on two orthogonal line defect waveguides

The transmission characteristics of a 2-dimensional (2D) square lattice photonic crystal waveguide (PCW) with an additional perpendicular line defect are investigated by the plane wave expansion method (PWM) and the finite difference time domain (FDTD) method. From simulation results and theoretical analysis, it is found that changing the refractive index of the dielectric columns in the additional line defect can effectively adjust the light transmission through the PCW. The working mechanism can be boiled down to either the excitation of a single defect mode or the contra-directional coupling of the two defect modes. And this mechanism can be used to design other tunable optical devices.     

Loss coefficients for blazed waveguide corrugations

The coupling between bound modes of a corrugated dielectric-slab waveguide and modes of the radiation continuum is analysed by a perturbation method. Loss coefficients that account for the power coupled into radiation modes by any Bragg order of corrugations with an arbitrary profile are determined for the bound modes. Agreement is found with published results for sinusoidal profiles. The proportion of power coupled out through each dielectric interface of the slab waveguide is also determined. When the corrugation has an asymmetric (blazed) profile and coupling to radiation modes is by the first Bragg order, more power can be coupled out through one interface than the other, even if the refractive indices of the cladding regions are equal. If the coupling is by a higher Bragg order, then the division of power can be considerably more unequal than for first-order coupling, with the greater proportion leaving the side of the waveguide opposite to that for first-order coupling. The ratio of the power coupled out the two sides varies cyclically with radiation wavelength.     

Dynamics of two-mode radiation in optical waveguides with strong mode coupling

Amplitude equations, as well as the effective dispersion and nonlinearity parameters, which define the dynamics of a wave packet formed by two strongly coupled modes, are derived with allowance for the frequency dependence of the linear mode coupling coefficient. These equations are used to study the onset of the modulation instability of the two-mode wave packet, soliton-like pulses, and compression modes. Unlike single-mode systems, the last two effects in optical waveguides may arise for both a negative and positive disper-sion of the waveguide material.     

条形耦合波导对光子晶体耦合缺陷模的影响

光子晶体的耦合缺陷模可以通过透射谱形状来表征,而透射谱形状则与连接缺陷的条形耦合波导相关.不同于直接耦合时信号相移只依赖于缺陷模的共振频率,当存在耦合波导时信号相移也决定于波导的长度和色散关系.随着波导长度的增加,透射谱形状发生从三峰到两峰,再到平项,最后又回到三峰的周期性变化.时间耦合模的分析表明,在缺陷模频率附近理论结果与时域有限差分法的计算结果完全一致,表明在此复杂情况下理论模型依然有效.     

Coupled mode analysis of light modulation in dielectric waveguides

A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO₃ crystal as a substrate is also described.     

Quasi-solitons of magnetostatic waves in a two-layer structure under single-mode excitation

We investigate the quasi-solitons of the envelope of forward body magnetostatic waves in a structure that consists of two magnetically coupled films separated by a nonmagnetic interlayer under the initial excitation of a pulse in one of them. We have found that as the pulse propagates, its energy is transferred from one film to the other through intermode coupling; as a result, “pulsating” quasi-solitons of the coupled modes of the two films emerge. We show that the amplitude of each of the mode pulses at the exit from the waveguide can be regulated over a wide range by varying the magnetizing field.     

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.     

基于包层模谐振的三包层石英特种光纤温度传感特性研究

提出了一种基于包层模谐振的光纤温度传感器. 它是通过将三包层石英特种光纤(TCQSF)两端分别与普通单模光纤(SMF)电弧熔接构成的SMF-TCQSF-SMF结构. 根据耦合模理论, 首先将TCQSF等效为三个同轴波导, 按各波导模场的分布特点标量计算其传输模式的色散曲线, 并深入研究其耦合长度与传输谱线之间的关系; 其次根据光纤的热光效应及热膨胀效应, 分析计算该传感器的温度灵敏度; 最后选取耦合长度为一个拍长时的传感器进行温度传感实验. 实验结果表明, 在35-95 ℃的温度变化范围内, 其温度灵敏度为73.74 pm/℃, 与理论计算结果一致. 因此, 该传感器具有结构简单、制备容易、灵敏度高、包层模激发可控等优点, 可用于工业生产、生物医学等温度传感领域.     

温度测量范围加倍的单微环传感器

本文提出了一种基于U形波导耦合单微环结构的新型SOI(绝缘体上硅)温度传感器.温度变化引起感温部位有效折射率和长度变化,导致传感器的输出光谱发生漂移.根据传输矩阵法和耦合模理论,设计了新型传感器模型,并且分析了感温部位不同时系统输出光谱特性.结果表明:当U形波导耦合单微环整体结构感温时,输出光谱无伪模,消光比达到31 dB,可作为最佳感温元件.相比于传统的双直波导耦合单微环结构,当U形波导的两个耦合点间的距离为微环周长的整数倍数时,FSR(自由光谱范围)可加倍至56 nm,灵敏度提高到89.2 pm/?C,测量范围为298—720 K,实现了SOI微环谐振器的高温测量.     

Distinguishing the Topological Zero Mode and Tamm Mode in a Microwave Waveguide Array

The Su–Schrieffer–Heeger (SSH) model has been the subject of extensive experimental research in the context of topological photonics. Ideally, the on‐site potential and hopping strength are sufficiently accurate for implementation in photonic coupled waveguide arrays. Here, two localized edge modes, the topological zero mode and trivial Tamm mode, are proposed and demonstrated in the modified SSH model using a microwave photonic waveguide array. The system used is composed of an array of evanescently coupled ultrathin corrugated metallic “H‐bar” waveguides. Furthermore, the differences between the zero mode and Tamm mode are clearly demonstrated by microwave near‐field experiments on the coupling behavior along the propagation direction for 40 cm at the excitation frequency of 17 GHz. These findings should deepen the understanding of localized edge mode confinement mechanisms, both in coupled waveguide array systems and other topological or quantum systems.     

Coupling effect of surface plasmon polaritons in single-negative lamellar heterostructure

Propagation characteristics of surface plasmon polaritons (SPPs) in the lamellar heterostructure, which is actually a SPP waveguide array, constructed by two kinds of single negative (SNG) material layers stacked alternatively are investigated. Based on the finite element method (FEM), the negative-refraction (NR) property is demonstrated when the electromagnetic wave penetrates through free space into such SNG lamellar structure. A clear view of the underlying physics of NR is presented qualitatively that is mainly related to the coupled SPPs. The strong coupling effect leads to the novel SPP dispersion curves and then the anomalous propagation characteristics.