Fabrication of blazed gratings by area-coded effective medium structures

Area-coded effective medium structures (ACES) are a recently presented novel type of diffractive structure. Because of their higher stability compared to 2D binary blazed gratings, they have the potential of a broader use in micro-optics applications. The first fabrication with electron-beam lithography validate the theoretical model of blazed ACES. The measured diffraction efficiencies are in very good agreement with the values obtained from rigorous electromagnetic analysis.     

光导板中新型衍射元件的数值模拟研究

基于严格耦合波理论,数值计算了一种在闪耀斜面镀膜的亚波长光栅结构,并首次提出将该光栅应用于光导板的设计中,使光导板衍射的RGB光束无需经过滤色片,直接透射相应的像素点。在数值计算中,设定入射光为TE偏振态、入射角为60°、波长为RGB三基色。光栅以有机玻璃为基底,二氧化钛为膜层,并随波长改变周期、闪耀角等参数。计算结果表明,该光栅的一级衍射光可垂直于表面出射,一级衍射效率随膜厚渐变,最高达37%,其余非零级次的衍射效率低于2%。将该特性的光栅应用于新型光导板的数值建模中,并对光栅的制作进行了工艺容差分析,计算得归一化能量的标准差小于1%,总衍射效率接近80%。     

Laser-induced grating self-diffraction from a medium with induced absorption

There are a great variety of optical nonlinearities that can lead to the phenomenon of laser-induced gratings (LIG) in semiconductors. In the present contribution the dynamic behaviour of an induced absorber with intrinsic bistability is investigated under excitation in a LIG self-diffraction arrangement. Using CdS as a model substance, the comparison of our theoretical model with our experimental findings gives an insight into the nonlinear dynamics of the degenerate carrier system and also an estimation of the transport properties of the electron-hole plasma.     

Dissipative structures in a continuous medium

Institute of Mining, Siberian Branch, Russian Academy of Sciences, Novosibirsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 94–104, April, 1992.     

双套管式光纤Bragg光栅温度传感器的仿真设计与研制

光纤传感器测量温度变化时为消除外加应力应变对温度产生的影响,设计了双套管式光纤Bragg光栅(FBG)温度传感器,双层结构用来隔离外加应力应变。对温度传感器建立平衡态模型,并进行有限元热分析,仿真结果分析表明,当温度从20℃跃变到70℃、70℃跃变到20℃时,温度响应时间分别为t0.9=50±1s、t0.9=60±1s。并与水浴法测温实验结果(t0.9=52s、t0.9=63s,灵敏度为9.8410-3nm/℃,线性度为99.88%)相比较,时间偏差小于3s。     

Analysis and design of a new type NRD-guide E-plane Y-junction circulator

A new type of E-plane Y-junction circulator has been developed based on the nonradiative dielectric waveguide (NRD-guide) in Ka- band. First, the circulation principle has been analysed by the theory of polarization wave. The field components in the nonreciprocal Y-junction zone and the conclusion of 60° phase difference between clockwise and counterclockwise rotating polarization modes has been obtained. And then, the resonant frequency of the non-dc biased triangle ferrite sample has also been calculated. This kind of structure is benefit to enlarge the bandwidth of the Y-junction circulator. As an example, we had designed and fabricated a circulator in Ka-band. Its operating frequency is 35. 1GHz, the 1.5dB insertion loss and 20dB isolation bandwidth is about 1. 0GHz.     

新型对开门高低温动态试验箱研制

介绍了新型对开门高低温动态试验箱的研制过程,包括系统热负荷计算、复叠制冷循环系统的热力计算等。并根据系统的热力计算,进行了冷凝器和蒸发器的结构设计以及主要部件压缩机和通风机的设计选型。     

Fabrication of grating structures with variable period

Photoresist gratings with variable period have been fabricated by recording the interference pattern of a collimated laser beam with a converging one. The period variation as a function of position, as well as the wavelength dependent focal properties of the gratings, has also been analyzed.     

Plasmonic electro-optic modulator design using a resonant metal grating

A plasmonic electro-optic modulator design using an evanescently coupled resonant metal grating is numerically studied in this Letter. Owing to excitation and propagation of long-range surface plasmons between the metal grating nanowires, a deep and narrow reflection dip can be obtained. Improved modulation performance is achieved through decreased damping from large dielectric gaps between the grating nanowires. An optimized electro-optic modulator design with lower insertion loss and low operating voltage is presented.     

Optimization design of flat-band long-period grating

We present a method to optimize the flat-band long-period fiber Bragg grating (FBG) in this letter.The method is based on the p~rticle swarm optimization method and the matrix transmission method.The optimized refractive modulation profile does not introduce so many phase shifts and is easier to fabricate compared with that of layer-peeling method which introduces lots of π phase shift at each zero point of apodization profile in designing for the same problem.     

Optimization design of flat-band long-period grating

We present a method to optimize the flat-band long-period fiber Bragg grating (FBG) in this letter. The method is based on the particle swarm optimization method and the matrix transmission method. The optimized refractive modulation profile does not introduce so many phase shifts and is easier to fabricate compared with that of layer-peeling method which introduces lots of π phase shift at each zero point of apodization profile in designing for the same problem.     

声光栅正弦结构光投射器的光学系统设计

针对一种新型的声光波干涉测量技术,对声光栅正弦结构光投射器的三维测量工作原理进行了系统的分析,讨论了影响投射器光学系统结构的因素和影响接收屏上的光照度的因素,并进行了光学系统设计。在优化设计过程中,采用了限制光线最大入射角的方法,达到控制投射系统的球差和保证接收屏上照明均匀的要求。所设计的声光栅正弦光投射器具有很好的成像质量。应用该系统对在500mm处的石膏像上投射干涉条纹,可以得到能量比较均匀、变形量很小的干涉条纹图,利用该条纹图和相关的算法可以对具有复杂几何形状的物体进行有效的三维测量。     

Analysis and design of grating couplers

Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The results cover TE_v and TM_v modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric profiles are also discussed.     

Nondestructive imaging of a type I optical fiber Bragg grating

Nondestructive images of refractive-index variation within a type I fiber Bragg grating have been recorded by the differential interference contrast imaging technique. The images reveal detailed structure within the fiber core that is consistent with the formation of Talbot planes in the diffraction pattern behind the phase mask that had been used to fabricate the grating.     

Realisation of an effective dual-parameter sensor employing a single fibre Bragg grating structure

A novel technology for simultaneous and independent measurement of dual parameters is proposed and experimented. The length of a single fibre Bragg grating (FBG) is divided into two parts. The temperature variation and another measurand can be measured independently and simultaneously, and the thermal effect can be erased with great ease.     

Stability of Bragg grating solitons in a cubic-quintic nonlinear medium with dispersive reflectivity

We investigate the existence and stability of Bragg grating solitons in a cubic-quintic medium with dispersive reflectivity. It is found that the model supports two disjoint families of solitons. One family can be viewed as the generalization of the Bragg grating solitons in Kerr nonlinearity with dispersive reflectivity. On the other hand, the quintic nonlinearity is dominant in the other family. Stability regions are identified by means of systematic numerical stability analysis. In the case of the first family, the size of the stability region increases up to moderate values of dispersive reflectivity. However for the second family (i.e. region where quintic nonlinearity dominates), the size of the stability region increases even for strong dispersive reflectivity. For all values of m, there exists a subset of the unstable solitons belonging to the first family for which the instability development leads to deformation and subsequent splitting of the soliton into two moving solitons with different amplitudes and velocities.     

Fabrication of large-area grating structures through laser ablation

A Grating-Interferometer setup is shown to be ideally suited for the fabrication of high quality periodic structures over large sample areas via laser ablation. Virtually perfect line structures with periods in the submicron range are easily obtained. The capabilities and limitations of the new setup are analyzed theoretically for nanosecond and femtosecond laser sources with different coherence properties. The theoretical predictions are verified experimentally for various sample materials.