Optimal design of sub-wavelength metal rectangular gratings for polarizing beam splitter based on effective medium theory

A novel optimal design of sub-wavelength metal rectangular gratings for the polarizing beam splitter （PBS） is proposed. The method is based on effective medium theory and the method of designing single layer antireflection coating. The polarization performance of PBS is discussed by rigorous couple-wave analysis （RCWA） method at a wavelength of 1550 nm. The result shows that sub-wavelength metal rectangular grating is characterized by a high reflectivity, like metal films for TE polarization, and high transmissivity, like dielectric films for TM polarization. The optimal design accords well with the results simulated by RCWA method.

Extraordinary optical transmission through metal gratings with single and double grooved surfaces

We investigate the transmission properties of a normally incident TM plane wave through metal films with periodic parabolic-shaped grooves on single and double surfaces using the finite-difference-time-domain method. Nearly zero transmission efficiency is found at wavelengths corresponding to surface plasmon excitation on a fiat surface in the case where the single surface is grooved. Meanwhile, resonant excitation of surface plasmon polariton （SPP） Bloch modes leads to a strong transmission peak at slightly larger wavelengths. When the grating is grooved on double surfaces, the transmission enhancement can be dramatically improved due to the resonant tunnelling between SPP Bloch modes.

Extraordinary Optical Confinement in a Silicon Slot Waveguide with Metallic Gratings

We present a silicon slot waveguide with metallic gratings embedded on the silicon surface in the slot region. The dependence of the optical coupling between two silicon wires on the width of the metal gap and the slot size are studied in detail. The results show that the optical field in the slot region with metallic gratings is significantly enhanced compared with the traditional slot waveguide due to the surface plasmon polaritons coupling on metallic gratings. The extraordinary optical confinement is attributed to the low effective dielectric constant of metallic gratings. The effective dielectric constant decreases with the increasing wavelength, and reaches the minimum when the width of the metal gap is about 0.01 times the wavelength.

光栅干涉式触觉传感器

因光学式触觉传感器有着灵敏度高、抗干扰能力强等优点,提出了一种基于亚波长金属光栅干涉的触觉传感器。首先,基于等效介质理论和薄膜干涉理论对触觉传感器的传感原理进行介绍;接着,通过纳米压印工艺和真空蒸发镀膜工艺在柔性中间聚合物片材(IPS)表面制作亚波长金属光栅,通过光刻工艺用SU—8光刻胶将亚波长金属光栅以固定间距平行离面放置,使其透射光强随接触力的施加而改变;最后,对光栅触觉传感器进行一系列力加载实验,实验结果表明:该触觉传感器的平均力分辨率可达到0.0003N/Gray以上,平均测量误差为6.3%。通过小型化设计,可以用于机械手上实现触觉传感功能。

金属光栅覆盖分布式布拉格反射镜结构的透射增强效应

为了采用易于直接激发的塔姆等离激元(Tamm plasmon polaritons,TPPs)实现透射增强现象,本文提出了一种由一维金属光栅覆盖分布式布拉格反射镜(distributed Bragg reflector,DBR)构成的层状结构.采用有限元法分析了入射光波在DBR-金属交界面上激发TPPs并产生能量高度局域的物理过程.研究表明入射TM光波在金属-DBR交界面上激发的TPPs可以有效地激发金属狭缝内的SPPs模式,当SPPs模式在狭缝内满足类FP谐振的条件就可以使入射光波在该结构中的产生透射增强.在此基础上,分析了狭缝宽度及其占空比对透射谱峰的定量影响.结果显示:周期确定时随着狭缝宽度的增大,峰值透射率则呈现先增大后减小的变化趋势;宽度确定时随着占空比的增大,峰值透射率会呈现单调降低的变化趋势,而透射峰中心波长呈现近似线性蓝移趋势,这为灵活调节异常透射的中心波长提供了一种有效手段.

低损耗超声波金属化光纤布拉格光栅传感特性研究

传统胶粘式表贴封装的光纤布拉格光栅(Fiber Bragg Grating,FBG)传感器在长期使用过程中易出现蠕变、老化等现象,采用性质稳定的金属材料代替高分子聚合物胶粘剂封装可解决上述问题。采用超声波焊接法对FBG进行全覆盖式封装,实现了超低损耗表贴式金属化封装结构,并研究了其温度和应变传感特性。结果表明:采用超声波焊接法进行金属化封装对FBG造成的传输损耗仅为0.04dB,封装后FBG传感器的温度灵敏度系数为26.44pm/℃,应变灵敏度系数为1.18 pm/με,温度和应变传感拟合R-Squared均达到0.9996以上。可见,采用超声波焊接法能够实现结构简单、传感性能可靠的低损耗金属化FBG温度和应变传感器的制作。

金属光栅增强石墨烯宽谱响应光电探测器

光电探测器在通信、检测和医疗等领域应用广泛,随着航空航天、夜视、遥感、热成像、汽车互联和消费电子等行业的发展,人们对超宽带探测器的需求也越来越迫切。现有的超宽带探测是使用不同材料、不同探测频段的多个光电探测器,集成度不高,阻碍了上述应用的发展。因此设计了石墨烯微米条–金属光栅复合结构的光电探测器,该器件在太赫兹、红外和可见光波段都可产生光电响应。在可见光范围内,金属光栅将探测器的探测灵敏度从1.1 mA/W显著提高至2.5 mA/W。该研究为基于石墨烯的超宽带光电探测器的设计提供了新的思路。

Effect of cyclotron resonance on ‘hot’ dispersion in a staggered double metallic grating sheet beam travelling wave tube

Based on the beam wave synchronous interaction in transverse and longitudinal directions at the same time and starting from Maxwell’s equation and linear Vlasov equation, the beam–wave interaction ‘hot’ dispersion equation considering both cyclotron resonance and Cherenkov resonance in a staggered double metallic grating traveling wave tube is deduced.Through the reasonable selection for geometric and electrical parameters, the numerical calculation and analysis of the ‘hot’ dispersion equation shows that the beam–wave interaction gain and frequency band with the cyclotron resonance enhancement effect are higher than those with only Cherenkov resonance radiation.

Dual bound states in the continuum enhanced second harmonic generation with transition metal dichalcogenides monolayer

The emergence of two dimensional(2D)materials has opened new possibilities for exhibiting second harmonic genera-tion(SHG)at the nanoscale,due to their remarkable optical response related to stable excitons at room temperature.However,the ultimate atomic-scale interaction length with light makes the SHG of Transition Metal Dichalcogenides(TM-Ds)monolayers naturally weak.Here,we propose coupling a monolayer of TMDs with a photonic grating slab that works with doubly resonant bound states in the continuum(BIC).The BIC slabs are designed to exhibit a pair of BICs,reson-ant with both the fundamental wave(FW)and the second harmonic wave(SHW).Firstly,the spatial mode matching can be fulfilled by tilting FW's incident angle.We theoretically demonstrate that this strategy leads to more than four orders of magnitude enhancement of SHG efficiency than a sole monolayer of TMDs,under a pump light intensity of 0.1 GW/cm^(2).Moreover,we demonstrate that patterning the TMDs monolayer can further enhance the spatial overlap coefficient,which leads to an extra three orders of magnitude enhancement of SHG efficiency.These results demonstrate remarkable pos-sibilities for enhancing SHG with nonlinear 2D materials,opening many opportunities for chip-based light sources,nano-lasers,imaging,and biochemical sensing.

Surface Plasmon Interference Lithography Assisted by a Fabry-Perot Cavity Composed of Subwavelength Metal Grating and Thin Metal Film

A surface plasmon interference lithography assisted by a Fabry-Perot （F-P） cavity composed of subwavelength metal gratings and a thin metal fihn is proposed to fabricate high-quality nanopatterns. The calculated results indicate that uniform straight interference fringes with high contrast and high electric-field intensity are formed in the resist under the F-P cavity. The analyses of spatial frequency spectra illuminate the physical mechanism of the formation for the interference fringes. The influence of the F-P cavity spacing is discussed in detail. Moreover, the error analyses reveal that all parameters except the metal grating period in this scheme can bear large tolerances for the device fabrication.

Surface plasmon resonance transmission filters at 1053 nm based on metallic grating with narrow slit

Metallic gratings with narrow slits can lead to special optical properties such as strongly enhancing the trans- mission and considerably strengthening the polarized effect. A narrow-band filter suitable for application in optical communication is designed by sandwiching a metallic grating between two identical dielectric films. The maximum transmission can reach 96% after optimizing the parameters of films and grating at a central wavelength of 1053 nm. It is the first time, to our knowledge, that such high transmission has been reported since the discovery of the extraordinarily high transmission through periodic holes or slits; moreover, the extremely polarized effect is also found in P mode of this symmetric grating.

Splitting the surface wave in metal/dielectric nanostructures

We investigate a modified surface wave splitter with a double-layer structure, which consists of symmetrical metallic grating and an asymmetrical dielectric, using the finite-difference time-domain （FDTD） simulation method. The metal/dielectric interface structure at this two-side aperture can support bound waves of different wavelengths, thus guiding waves in opposite directions. The covered dielectric films play an important role in the enhancement and confinement of the diffraction wave by the waveguide modes. The simulation result shows that the optical intensities of the guided surface wave at wavelengths of 760-nm and 1000-nm are about 100 times and 4-5 times those of the weaker side, respectively, which means that the surface wave is split by the proposed device.

ANALYSIS OF DISPERSION CHARACTERISTICS FOR A CIRCULAR DIELECTRIC WAVEGUIDE WITH PERIODIC METALLIC STRIPS

The dispersion characteristics of a circular dielectric waveguide with periodic metal-lic strips are analyzed by the Galerkin’s method.After obtaining the rigorous dispersion equation,the dispersion curves for both TE01and TM01modes are calculated by the improved Newton’smethod.The variations of the normalized center frequency,width and maximum attenuation con-stant of the stopband with the normalized width of the metallic strips are given.The convergenceproperties of numerical solutions are also discussed.On the basis of the analysis,some usefulguidelines for filter design are thereby suggested.

Optical phase front control in a metallic grating with equally spaced alternately tapered slits

A technique capable of focusing and bending electromagnetic （EM） waves through plasmonic gratings with equally spaced alternately tapered slits has been introduced. Phase resonances are observed in the optical response of transmission gratings, and the EM wave passes through the tuning slits in the form of surface plasmon polaritons （SPPs） and obtains the required phase retardation to focus at the focal plane. The bending effect is achieved by constructing an asymmetric phase front which results from the tapered slits and gradient refractive index （GRIN） distribution of the dielectric material. Rigorous electromagnetic analysis by using the two-dimensional （2D） finite difference time domain （FDTD） method is employed to verify our proposed designs. When the EM waves are incident at an angle on the optical axis, the beam splitting effect can also be achieved. These index-modulated slits are demonstrated to have unique advantages in beam manipulation compared with the width-modulated ones. In combination with previous studies, it is expected that our results could lead to the realization of ootimum designs for plasmonic nanolenses.

Numerical analysis of surface plasmons excited on a thin metal grating

The authors numerically investigated the characteristics of surface plasmons excited on a thin metal grating placed in planer or conical mounting. After formulating the problem, the solution method, Yasuura＇s method （a modal expansion approach with least-squares boundary matching） was described. Although the grating is periodic in one direction, coupling between TE and TM waves Occurs because arbitrary incidence is assumed. This requires the employment of both TE and TM vector modal functions in the analysis. Numerical computations showed： （l） the excitation of surface plasmons with total or partial absorption of incident light; （2） the resonance character of the coefficient of an evanescent order that couples the plasmon surface wave; （3） the field profile and Poynting＇s vector. The plasmons excited on the surfaces of a thin metal grating are classified into three types： SISP, SRSP, and LRSP, different from each other in the feature of field profile and energy flow. In addition, the eigenvalue of a plasmon mode was obtained by solving a sequence of diffraction problems with complex-valued angles of incidence and using the quasi-Newton algorithm to predict the real angle of incidence at which the absorption occurs.

Application of CCD Technique to Stress and Strain Measurements of Metals

Crossed grating stuck to metal surface was used as a strain sensor in the present work, and stress as well as strain were then investigated by accurately determining the change in the position of diffraction spot before and after deformed. A hardware testing system for linear CCD array, data gathering and processing was therefore developed for this purpose. Experimental results showed that the system has a good accuracy and can be used to measure stress and strain of metal surface in a real-time and quantitative manner.

Optimization of Duty Ratio of Metallic Grating Arrays for Infrared Photodetectors

Influence of duty ratio of metallic gratings applied in quantum well infrared photodetector (QWIP) with detection ranging from 3 &#956m to 5 &#956m was studied in this paper. The influence on longer enhanced wavelength working at infrared waveband was investigated. A relationship between the duty ratio and the enhanced peak intensity is given. Some results can be applied to optimize the enhanced efficiency of the metallic gratings.

Fabrication of Polarization Control Devices Using Metal Grating Structures

A polarization control device was developed using a plasmonic metasurface with the aim of achieving the desired polarization state. In this study, the Ag metal grating structure was fabricated as a plasmonic metasurface by electron beam lithography and a lift-off process. The phase difference of the fabricated sample was 21.0°. This value is almost consistent with the simulation (24.0°). Then, the transmission and phase difference is dependent on the structural parameter. Because of the propagation of surface plasmon polariton at the interface between Ag and SiO2 or Ag and air, it is believed that the transmittance and the phase difference for TM polarized light can be controlled by the structural parameters. By plotting on the Poincaré sphere after calculating the S-parameter by simulation, it is clear that the arbitrary polarization status can be controlled by the structural parameter.

Sensing characteristics of a metal film coated long-period fiber grating

To obtain the influence rules of the coating parameters of a long-period fiber grating(LPFG)with respect to temperature,strain and refractive index sensing properties,based on the mode coupling theory,a strict four-layer theorietical model of a metal film coated LPFG is established,and these parameters that affect the spectral characteristics of the metal film coated LPFG are studied.The simulation results show that there is an optimal metal film thickness on the surface of the LPFG that will induce the surface-plasmon resonance(SP R)effect,which results in higher sensitivity to the environmental temperature and refractive index but has little influence on the strain There is theoretical evidence that when the silver thickness is between0.8and1.2nm,the refractive index sensitivity will reach the peak point of42.4026,at which the refractive index sensor sensitivity is increased by4.S%.The theoretical results of coating a long-period fiber grating provide a good theoretical basis and guidance for LPFG design and parameters optimization

基于FPGA与CMOS图像传感器的集成式偏振导航传感器

偏振导航传感器以天空偏振光场为导航信息源,具有无源自主、实时性好、无误差累积等优点。以互补金属氧化物半导体(CMOS)图像传感器作为光电转换器件,可以解决基于光电二极管的偏振导航传感器易受干扰的问题。基于集成了六方向金属纳米光栅的CMOS图像传感器,以现场可编程门阵列(FPGA)为处理核心设计了仿生偏振导航传感器。首先,阐述了偏振导航传感器的工作原理与传感器有效数据提取算法;其次,设计了传感器的软硬件系统,在FPGA上开发了偏振信息图像的采集模块、数据筛选模块以及数据处理模块,可以实时解算出偏振角,并通过串口输出;最后对传感器性能进行了实验验证。结果表明,该传感器可以实时输出偏振角度,且最大角度误差为0.1°。