Two-dimensional non-spatial filtering based on holographic Bragg gratings

The filter made up of two gratings performs as a two-dimensional non-spatial filtering. This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer. Diffraction efficiency of a single grating is up to 78% in Bragg＇s condition, then a two-dimensional non-spatial filter, which consists of two volume Bragg gratings and a half-wave plate, enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%. The Bragg＇s condition and effect of polarisation on performances of the two-dimension filter are also discussed.

Two-Dimensional Talbot Effect with Atomic Density Gratings

We report the experimental observation of two-dimensional Talbot effect when a resonance plane wave interacts with a two-dimensional atomic density grating generated by standing wave manipulation of ultracold Bose gases. Clear self-images of the grating and sub-images with reversed phase or fractal patterns are observed. By calculating the autocorrelation functions of the images, the behavior of periodic Talbot images is studied. The Talbot effect with two-dimensional atomic density grating expands the applications of the Talbot effect in a wide variety of research fields.

Monitoring shear deformation of sliding zone via fiber Bragg grating and particle image velocimetry

Monitoring shear deformation of sliding zones is of great significance for understanding the landslide evolution mechanism,in which fiber optic strain sensing has shown great potential.However,the cor-relation between strain measurements of quasi-distributed fiber Bragg grating(FBG)sensing arrays and shear displacements of surrounding soil remains elusive.In this study,a direct shear model test was conducted to simulate the shear deformation of sliding zones,in which the soil internal deformation was captured using FBG strain sensors and the soil surface deformation was measured by particle image velocimetry(PIV).The test results show that there were two main slip surfaces and two secondary ones,developing a spindle-shaped shear band in the soil.The formation of the shear band was successfully captured by FBG sensors.A sinusoidal model was proposed to describe the fiber optic cable deformation behavior.On this basis,the shear displacements and shear band widths were calculated by using strain measurements.This work provides important insight into the deduction of soil shear deformation using soil-embedded FBG strain sensors.

Non-diffracting integer-order and half-integer-order carpet beams obtained by even-type sinusoidal amplitude radial gratings

In this work,we introduce a kind of new structured radial grating,which is named the even-type sinusoidal amplitude radial(ETASR)grating.Based on diffraction theory and the principle of stationary phase,a comprehensive theoretical investigation on the diffraction patterns of ETASR gratings is conducted.Theoretical results show that novel carpet beams with beautiful optical structures and distinctive characteristics have been constructed on the basics of the ETASR grating.Their diffraction patterns are independent of propagation distance,that is,the new carpet beams have diffraction-free propagating characteristics.The non-diffracting carpet beams are divided into two types by beam characteristics:non-diffracting integer-order and half-integer-order carpet beams.Subsequently,we experimentally generate these carpet beams using the ETASR grating.Finally,their particularly interesting optical morphology and features are explored through numerical simulations and experiments.

Influence of Surface Geometry of Grating Substrate on Director in Nematic Liquid Crystal Cell

The director in nematic liquid crystal cell with a weak anchoring grating substrate and a strong anchoring planar substrate is relative to the coordinates x and z.The influence of the surface geometry of the grating substrate in the cell on the director profile is numerically simulated using the two-dimensional finite-difference iterative method under the condition of one elastic constant approximation and zero driven voltage.The deepness of groove and the cell gap affect the distribution of director.For the relatively shallow groove and the relatively thick cell gap,the director is only dependent on the coordinate z.For the relatively deep groove and the relatively thin cell gap,the director must be dependent on the two coordinates x and z because of the increased elastic strain energy induced by the grating surface.

Composite Sinusoidal Nanograting With Long-Range SERS Effect for Label-Free TNT Detection

A composite one-dimensional （1D） Ag sinusoidal nanograting aiming at label-free surface enhanced Raman scattering （SERS） detection of TNT with robust and reproducible enhancements is discussed. 1D periodic sinusoidal SiO2 grating followed by Ag evaporation is proposed for the creation of reproducible and effective SERS substrate based on surface plasmon polaritons （SPPs）. The optimal structure of 1D sinusoidal nanograting and its long-range SERS effect are analyzed by using the finite difference time domain （FDTD）. Simulation SERS enhancement factor （EF） can be 5 orders of magnitude as possible. This SERS substrate is prepared by the interference photolithography technology, its SERS performance is tested by Rh6G detection experiments, and the actual test EF is about 10. The label-free SERS detection capacity of TNT is demonstrated in the experiment.

Polarization diversity two-dimensional grating coupler on x-cut lithium niobate on insulator

We propose and demonstrate a polarization diversity two-dimensional grating coupler based on the lithium niobate on insulator platform, for the first time, to the best of our knowledge. The optimization design, performance characteristics,and fabrication tolerance of the two-dimensional grating coupler are thoroughly analyzed utilizing the three-dimensional finite-difference time-domain method. Experimentally,-7.2 d B of coupling efficiency is achieved with 1 d B bandwidth of64 nm. The polarization-dependent loss is about 0.4 d B around 1550 nm. Our work provides new polarization multiplexing approaches for the lithium niobate on insulator platform, paving the way for critical applications such as high-speed polarization multiplexed electro-optical modulators.

Optical true time-delay for two-dimensional phased array antennas using compact fiber grating prism

A two-dimensional(2D) optical true-time delay(TTD) beam-forming system using a compact fiber grating prism(FGP) for a planar phased array antenna(PAA) is proposed. The optical beam-forming system mainly consists of a TTD unit based on the same compact FGP, one tunable laser for elevation beam steering, and a controlled wavelength converter for azimuth beam steering. A planar PAA using such 2D optical TTD unit has advantages such as compactness, low bandwidth requirement for tunable laser sources, and potential for large-scale system implementations. The proof-of-concept experiment results demonstrate the feasibility of the proposed scheme.

The property research of the transmission sinusoidal grating with fabrication of LIGA process

The transmission sinusoidal grating(TSG) shows a different diffraction pattern with conventional black-white transmission grating(BWTG), which can focus the diffraction energy on a higher order and has been widely used in the spectrum instruments. According to the description of the scalar diffraction theory, the numerical simulation for diffraction properties of the TSG has been studied for years. However, the fabrication of the TSG is difficult and seldom reported. In this article, a TSG is designed and an approach of the X-ray LIGA process is used to fabricate the TSG and the device can obtain the brightest diffraction peaks at the ±1 order with the zero-order diffraction peak unobvious on the background for a certain wavelength of the incident light.

椭偏法测光栅参数的可行性理论研究

提出一种新的光栅测试方法———利用椭偏仪测量光栅的基本参数 ,同时将求解优化问题的正单纯形法用来反演光栅的椭偏方程。首先假设一种光栅模型 ,计算出不同入射角的椭偏参数 (Δ ,Ψ) ,然后加入偏差量不同的高斯噪声 ,把加入噪声后的值 (Δm,Ψm)作为模拟测量值 ,采用正单纯形法进行求解。验证得知由这种方法求得的光栅参数接近假设的光栅参数值。反演结果表明 ,在扩大搜索范围时 ,仍可以在一定精度范围内得到准确解 。

基于正弦透射光栅的激光告警接收机研究

在光电对抗中,高速、可靠地获取敌方来袭激光的参数是实施有效对抗的关键。提出了基于正弦振幅透射光栅衍射原理的窄脉冲激光波长和入射方向的测试方法,并设计了激光告警接收机原理样机,该样机由光栅、平凸柱面镜、ATMEL公司的驱动频率为50MHz的线阵CCD探测器、高速数字信号处理器TMS320V C5509和液晶显示电路构成。结果表明,该样机可达到如下技术指标:波长范围为500～1100nm、波长分辨率≤10nm、视场范围为22.5°、角度分辨率≤1°、反应时间<0.1s、灵敏度<10mW/cm2。

用亚波长正弦介质光栅设计1/4波片

采用扩展边界条件法 ,得出亚波长正弦介质光栅正入射反射型 1/ 4波片的结构参数。发现在一定精度范围内TE波与TM波的相位差能够在一段较大的槽深区域满足设计要求 ,从而降低了实际控制刻蚀深度的难度。讨论了线偏振光转化为圆偏振光的方位角问题。

利用正弦光栅探测激光信息的理论研究

利用傅里叶变换理论研究了激光以任意角度入射正弦光栅的夫琅和费衍射,并对衍射图像的相对光强分布进行了分析,得到了零级和正负一级明纹中心位置与入射激光信息之间的关系以及对应的明纹宽度。通过数据处理,反向推导出了入射激光的波长和方向与明纹位置的关系,进而获得了计算入射激光参数的方法。根据计算结果提出了采用CCD观测衍射图像、利用DSP高速采集信号和单片机处理数据的样机设计方案。在对样机各类参数进行了论证的基础上,推算了样机性能。

投影系统中高质量全息正弦光栅的研制

为了解决结构光三维测量系统中对高质量全息正弦光栅的要求,文章提出了一种高质量正弦光栅的制作方法,该方法可以方便地精确调整所需要的条纹频率和在线观测条纹质量;制作的光栅条纹平行度及均匀性好,光栅常数控制精确,而且畸变小,能获得良好的正弦性条纹分布。

干涉成像系统传递函数的数值分析(英文)

干涉仪系统传递函数能有效地表征系统相位成像的性能。通过假设干涉成像系统是复振幅的线性平移不变系统,模拟计算正弦相位光栅和相位台阶这两类标准相位物体的成像,确定干涉仪系统传递函数。数值分析结果表明:系统传递函数随着波像差的增加而减小;干涉成像系统对小幅度相位(远小于1 rad)成像是近似线性的,而对大幅度相位(大于0.5 rad)成像则是明显非线性的。当正弦相位的幅度为1时,系统传递函数在1/2和1/3截止频率处出现明显的急剧下降。高度为π/2的相位台阶成像时,系统传递函数随着空间频率的增加而缓慢地降低。

光栅衍射空间滤波产生正弦光强靶标的方法

在光学测试、光学信息处理及相关交叉学科的各个领域,都需要用到正弦光强靶标,但是制作正弦光栅比较困难.根据阿贝成像理论的光学傅里叶分析原理,设计了"V"形空间滤波器,并利用激光和光学空间滤波器产生了正弦光强靶标,对正弦光强靶标进行了采集和分析,达到了预期的效果,获得了较为理想的正弦光强靶标.

空间滤波实验的改进

根据阿贝成像的基本原理 ,利用一系列特殊光路 ,使物体不同部分“着上”不同的颜色 ,并且可以使物体各部分着上的颜色通过滤波器相互转换 .

用非相干光相移—投影格栅法测量三维物体表面轮廓

本文利用非相干光投影格栅相移技术,建立了一套可准确测量三维物体表面形状的自动系统.为精度为几百微米至几十微米的形状测量提供了一种高精度便捷的方法.文中分析了误差因素,给出了系统标定的结果和部分实测实例.结果表明,本文的系统和方法实用简便、高精度、自动化.

高密度全场主动离焦三维测量的精度分析

向物体投射正交正弦光栅或正弦光栅,都能实现我们提出的高密度全场离焦三维测量,实验发现测量精度依赖于投射模式和物体表面纹理。计算机模拟显示物体深度测量精度与物体纹理的调制度、频率和投射光栅方向有关。对各种纹理,正交正弦光栅投射的测量精度都高于正弦光栅投射的测量精度。在相同实验条件下,正交正弦光栅和正弦光栅投射的弱纹理表面的深度测量均方误差分别为0.18mm和0.25mm,较强纹理表面的均方误差为0.35mm和0.54mm。

特定方位的光栅识别学习不改变猫外膝体背核神经元的方位敏感性

视觉信号识别训练可改变视觉通路神经元的可塑性, 其神经机制尚不清楚。已有少数研究显示, 动物(猴) 长时间进行特定方位的光栅识别学习后, 视皮层部分神经元对视觉刺激的反应表现出与学习任务相关的敏感性变化。这种敏感性变化是否亦存在于皮层下结构尚无报道。本实验训练两只成年猫分别进行水平和垂直方位的条形静止正弦光栅的识别以获得食物奖赏, 两只猫的行为识别能力逐渐提高, 4 个多月后识别的正确率达85%以上, 用与训练方位垂直的正弦光栅检测发现, 识别正确率明显下降。细胞外记录外膝体背核(Dorsal lat eral geniculate nucleus, dLGN) 神经元对不同方位正弦光栅刺激的反应显示, 与正常猫相比, 训练猫外膝体细胞的最优方位并未向着训练方位发生明显改变, 对于感受野位于中央区15度视角以内的细胞来说, 其方位选择性强度以及在训练方位的发放强度与正常猫无明显差异。以上结果表明, 猫对特定方位的光栅识别学习不改变外膝体神经元的方位敏感性, 其行为上方位识别特异性的提高可能与视皮层细胞的方位编码可塑性有关。