Lossy double negative guiding layer optical sensors

We proposed a three-layer waveguide as an optical sensor for homogeneous sensing applications. A guiding layer of the proposed structure is considered as lossy left-handed material (LHM) with simultaneously the complex negative electric permittivity ɛ and the complex negative magnetic permeability μ. We also assume a cladding layer to have an intensity-dependent refractive index. Sensitivity of the proposed optical waveguide sensor is derived and its dependence on different parameters of a waveguide is studied.     

Optimization of transverse electric peak-type metal-clad waveguide sensor using double-negative materials

In a very recent work, a transverse electric peak-type metal-clad waveguide optical sensor was proposed in which a double-negative material (DNM) was used as a guiding layer. The sensor was found to exhibit a considerable angular shift of the reflectance peak for small changes in the refractive index of the analyte, due to the DNM layer. In this work, the optimization of the structure parameters is investigated to find out the most appropriate metal and its optimal thickness. Moreover, the optimal DNM layer parameters corresponding to the highest sensitivity are explored. Our calculations reveal that metals with high absolute value of the real part of the permittivity correspond to sharper peaks. Moreover, as the absolute value of the real part of both ε and μ of the DNM increases, the reflectance peak becomes sharper and the dip following the peak becomes deeper.     

Enhancement of sensitivity in optical waveguide sensors using left-handed materials

We show analytically that the sensitivity of an optical waveguide sensor can be dramatically enhanced by using a metamaterial with negative permittivity and permeability. The variation of the sensitivity of the proposed waveguide sensor with different parameters of the waveguide is studied. It is found that the sensitivity of the sensor increases with the increasing thickness of the metamaterial due to the surface polariton generation.     

波导型钯(Pd)膜氢传感器数值模拟及优化

基于离子交换波导的集成型器件是氢敏传感器中很有发展潜力的一种. 传感区域由离子交换波导及其表面的金属钯膜组成, 通过有限差分法（FDM）计算了这种波导结构中的导模及表面等离子模的模场分布, 分析了其传播特性与钯膜光学常数的关系, 并结合束传播方法（BPM）对钯膜的厚度进行了优化, 使其具有最高的灵敏度.     

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.     

Nonlinear dispersion equation and guided modes in a slab waveguide composed of a negative-index medium

We consider a slab waveguide made of a material with negative permeability and negative permittivity, the surrounding medium is conventional. By using the dispersion relation, we show the dispersion curves from the variation of the core width and other physical parameters. The associated energy flow for several thicknesses of the nonlinear layer waveguide is presented. We discuss possible new types of modes that can occur. It is found that the dispersion curves and the energy flow can be controlled by varying the thickness of the guide, the filling factor and the effective plasma frequency. A numerical simulation is done to well illustrate.     

带有多孔二氧化硅间隔层的导模共振光栅实现染料激光器发射增强

导模共振光栅是一种典型的平面波导共振结构,可在光栅表面或波导层内形成较强的局域电场,能增强光与物质的相互作用.本文在导模共振结构的光栅层和基底层之间,引入低折射率的多孔二氧化硅间隔层,显著增强了局域电场与增益介质的接触度.结果表明,引入多孔二氧化硅后,共振产生的电场增强区域上移至激光染料层,增加了激光染料与电场的相互作用,实现了激光出射增强.本文基于时域有限差分法,对结构参数进行分析优化,研究了820 nm共振波长激发下的出射激光特性,得到了连续的激光出射,其能量阈值约为2.5 mJ/cm^2,线宽约为0.3 nm.本文提出的结构实现了对表面局域电场的有效调控,增强了激发光与增益介质的相互作用,不但可应用于激光器,还为其它发光器件的设计提供了参考.     

一种双开口谐振环结构的新型双负介质

 提出了一种双开口谐振环结构的新型双负介质单元模型,该模型集电、磁谐振于一体,结构简单。用时域有限差分法和CST软件对该新型结构进行了模拟对比,并对其物理机理进行了分析,解释了其双负效应发生的原因。从电磁波理论出发,导出了波导中双负介质参数的反演公式,推广了通常提取介质参数的NRW方法,并由此提取了新型双负介质的等效电磁参数。结果表明：在频率10.3 GHz附近其等效介电常数和等效磁导率的实部同时为负值,确定了其双负效应的存在。     

Investigation of the limit of lateral beam shifts on a symmetrical metal-cladding waveguide

This paper reports that Goos--H\"anchen (GH) shifts occurring on a symmetrical metal-cladding waveguide are experimentally identified. It was found that there exists a critical thickness of the upper metal layer, h_cr, above which negative shift is observed and, reversely, positive shift occurs. Both positive and negative GH shifts near the critical thickness do not vary dramatically and can achieve a maximum on the submillimeter scale, which is different from simulated results using the stationary-phase method. It also shows that this critical thickness, h_cr, can be obtained at the position for zero reflectivity by setting the intrinsic damping to be the same as the radiative damping. The GH effects observed near the critical thickness are produced by extreme distortion of the reflected beam profiles, which limits the amplitude of the GH shift and, further, the sensitivity of the GH optical sensor based on the symmetrical metal-cladding waveguide.     

Optical sensors based on Fabry–Perot resonator and fringes of equal thickness structure

We propose theoretically two optical sensor structures based on Fabry–Perot resonator and fringes of equal thickness structure. Different from the conventional slab waveguide sensors in which the sample interacts with the evanescent field in the cladding layer, the proposed sensors contain the sample in the core layer. The first proposed sensor comprises a piezoelectric material as a substrate with the driving potential difference as the sensing probe for refractive index changes of the sample. The second sensor comprises fringes of equal thickness structure with the number of fringes per unit length is the probe for changes in the index of the sample. The calculations reveal that the proposed sensors have high sensitivity to changes in the refractive index of the sample.     

Metallic nonlinear magnetooptical nonreciprocal isolator

In advanced optical fiber communication systems where reflection light might cause degradation of the signal quality, optical waveguide isolators play an important role. The effect of a metal layer with negative permittivity on the behavior of nonlinear-magnetooptic isolator is studied. The isolator consists of metal film, nonlinear cladding, and magnetooptic substrate. It is found that difference between forward and backward propagation for TM₀ mode increases with increasing the absolute value of the tuning parameter which is the permittivity of the metal film, ?_f. It is also found that the maximum cut-off thickness of the isolator occurs in self-defocusing case around η = 0.65 and at the highest assumed value of ?_f = −8. These results are helpful in fabricating an isolator with high performance.     

左手介质椭圆光波导基模传播特性

在椭圆柱坐标系中,采用分离变量方法,得出了左手介质椭圆光波导本征方程的近似解,通过数值计算,分析了椭圆波导偏心率、左手介质的电容率、磁导率对椭圆光波导基模传播特性的影响,并将左介质光波导与右手介质光波导基模特性进行对比,得出左手介质光波导的基模特性与右手介质光波导基模特性差别不大的结论.     

Optical metamaterials at near and mid-IR range fabricated by nanoimprint lithography

Two types of optical metamaterials operating at near-IR and mid-IR frequencies, respectively, have been designed, fabricated by nanoimprint lithography (NIL), and characterized by laser spectroscopic ellipsometry. The structure for the near-IR range was a metal/dielectric/metal stack “fishnet” structure that demonstrated negative permittivity and permeability in the same frequency region and hence exhibited a negative refractive index at a wavelength near 1.7 μm. In the mid-IR range, the metamaterial was an ordered array of fourfold symmetric L-shaped resonators (LSRs) that showed both a dipole plasmon resonance resulting in negative permittivity and a magnetic resonance with negative permeability near wavelengths of 3.7 μm and 5.25 μm, respectively. The optical properties of both metamaterials are in agreement with theoretical predictions. This work demonstrates the feasibility of designing various optical negative-index metamaterials and fabricating them using the nanoimprint lithography as a low-cost, high-throughput fabrication approach. PACS 42.25.Bs; 81.16.Nd; 42.70.-a; 81.07.-b     

Light transmission along a slab waveguide with a core of anisotropic metamaterial

We investigated the dispersion property of a slab waveguide with an anisotropic metamaterial core whose permittivity tensor is partially negative. The subwavelength guidance characteristics are presented based on the boundary conditions. The results show that, at some specific frequencies, many high-order modes can exist in present waveguide even with the thickness of the guiding core 10 times smaller than the working wavelength. It is also found that different orientations of the optical axis of the anisotropic core will lead to different dispersion of the guided modes. If the orientation of the optical axis is properly chosen, the guided modes show a transition from backward wave to a forward wave as the frequency increases. During this transition, the group velocity of some guided modes can approach zero. Since the anisotropic metamaterial we discuss here can be fabricated in GHz, near- and mid-infra-red frequencies, our result may find some applications in wave trapper, integrated optical and nanophotonic devices.     

Analysis of surface and guided wave plasmon polariton modes in insulator–metal–insulator planar plasmonic waveguides

Theoretical and experimental study of the surface plasmon–polariton and guided wave plasmon polariton modes is presented for the Sapphire/Ag/Polycarbonate/Air structure. Theoretical results are obtained by solving complex multilayer eigenvalue equations as well as the reflectivity equation for this structure. It is proposed that the mode attenuation can be significantly reduced by inserting a low index dielectric buffer between the metal and the guiding dielectric layer. The dispersion and attenuation curves are generated. Both the surface plasmon and guided wave plasmon polariton modes are studied experimentally. The experimental values of the effective refractive indices agree well with the theoretical values. The electric field profiles are generated and used to examine the nature of modes. After optimization of various parameters the condition for low loss single mode guiding is obtained for the proposed structure. Effect of metal thickness on surface plasmon mode is also discussed. It is inferred that in a properly optimized plasmonic waveguide, the losses can be reduced by a factor of 4.     

Theoretical modeling of a nonlinear asymmetric metal-clad planar waveguide based sensors

The present paper deals with the theoretical modeling of a nonlinear asymmetrical metal-clad planar waveguide for sensor application to achieve high sensitivity. We take the appropriate field distributions for the proposed structure and impose the boundary conditions to derive the mode equation and other necessary formulae for the proposed sensor. The effect of nonlinearity on the sensitivity of the waveguide is studied. Also, we have compared our computed results with the results given for a similar sensor having five layers structure. It is observed that the sensitivity of the sensor is improved by introducing a nonlinear material in the cover medium.     

Double negative in flexural single metal layer at visible frequencies

We theoretically investigate a thin single metal layer covered on sub-wavelength dielectric grating. Numerical simulations show that the structure has negative index in the normal direction at visible frequencies. Structural investigation demonstrates that the simultaneous negative permittivity and permeability at an overlapping frequency range are attributed to the metal cut-wire and “U”-shaped structure disassembled from the structure, respectively. Furthermore, parametric exploration for practical fabrication is presented.     

Analytical sensitivity and reflected power through a D-shape optical fibre sensor

In this paper, the reflection properties and sensitivity of a D-shape optical fibre sensor are investigated theoretically and numerically with the emphasis on the metal layer [gold (Au), silver (Ag), copper (Cu), and aluminum (Al)]. Maxwell’s equations are used to determine the electric and magnetic fields of the incident waves at each layer. Snell’s law is applied and the boundary conditions are imposed at each layer interface to calculate the reflected power and sensitivity of the sensor. In the numerical results, the mentioned power is computed and illustrated as a function of wavelength, angle of incidence, metal layer thickness and refractive index of the external medium when the metal layer changes. The variation of sensitivity with the wavelength of the incident radiations is also proposed for some of the given metals.     

基于双十字架型宽带低耗小单元左手材料的设计与实验验证

提出了一种利用电谐振器与磁谐振器集成于一体的单面左手介质结构设计方案, 该方案采用两个十字架型金属结构镜像并列放置在介质基板的同一侧形成一个左手单元, 并将其排列成周期结构. 软件仿真和优化提取了一系列有效电磁参数, 结果表明, 该结构在9.4–16 GHz的频率范围内等效介电常数和等效磁导率同时为负, 其相对带宽达到了52%, 并且单元电长度和损耗都小于同类型的结构. 对该结构进行了加工、制作并通过波导法测试再次证明了其优良左手特性的存在性. 为左手材料的广泛应用打下了基础.     

Interferometric optical isolator with Si guiding layer fabricated by wafer bonding

An interferometric optical isolator, with a Si guiding layer, employing a nonreciprocal phase shift was studied. The optical isolator was comprised of a magneto-optic waveguide with a magnetic garnet/Si/SiO₂ structure, which was fabricated by wafer bonding technique. The nonreciprocal phase shift in the magneto-optic waveguide with the Si guiding layer was calculated at a wavelength of 1.55 μm. Several kinds of layer structures in the magneto-optic waveguide were discussed.