线偏振高斯光束通过条形浮雕光栅的传输

使用角谱表示和严格的模式理论研究了线偏振高斯光束通过特征尺寸与波长可比拟的条形浮雕光栅的传输，系统参数误差对浮雕层中光强最大值的影响.研究表明，光束在条形浮雕光栅各层中有不同的光强分布，浮雕层的介质填充部分中的光强明显高于展空部分的光强.光栅周期误差对浮雕层中最大光强的影响起主要作用.并利用模拟退火优化算法优化系统参数以控制出射光束的光强分布.     

线偏振高斯光束通过复合型衍射光栅的传输特性

提出一种集合浮雕和折射率周期分布调制的复合型衍射光栅,并利用角谱表示和严格的模式理论研究了线偏振高斯光束通过这种复合型衍射光栅的传输特性.数值计算结果表明,在光栅的同一透射深度处复合型衍射光栅光强的起伏频率要比浮雕型光栅光强的起伏频率小.最后使用复合型衍射光栅模型,研究了亚波长体积相位全息光栅的表面起伏和入射光束的束腰宽度对衍射效率的影响. 关键词： 复合型衍射光栅 亚波长体积相位全息光栅 高斯光束 严格模式理论     

基于多层介质膜光栅的谱合成系统光束特性分析

针对多层介质膜光栅在光束谱合成系统中的应用, 利用光线追迹方法, 建立了基于多层介质膜光栅的谱合成系统光传输模型. 多层介质膜光栅引入的相位调制包括浮雕表面上光程差与浮雕结构光程差两部分, 且受到光栅槽深、占空比和光束入射角等因素的影响. 利用衍射积分方法和光束非相干叠加原理, 计算模拟了基于多层介质膜光栅的谱合成系统的合成光束光强分布. 在此基础上, 利用强度二阶矩方法分析了合成光束的光束质量, 并讨论了多层介质膜光栅的槽深、占空比和制作误差等因素对合成光束特性的影响. 结果表明: 改变多层介质膜光栅的槽深和占空比以及中心光束入射角会影响合成光束能量, 但不会影响合成光束的光束质量, 合成光束的光束质量始终保持与单个子光束的光束质量相当; 多层介质膜光栅的制作误差对合成光束的光束质量和能量均存在明显影响.     

广义双曲正弦-高斯光束的Gyrator变换性质和暗空心光束产生

基于Gyrator变换,推导了广义双曲正弦-高斯光束场分布的解析表达式,研究了广义双曲正弦-高斯光束在Gyrator变换平面上的光强分布和相位特性.结果表明,在Gyrator变换过程中,具有边缘位错相位特性的双曲正弦-高斯光束能转换为具有涡旋的暗空心光束,并确定产生的暗空心光束的拓扑荷指数为一,而不具有边缘位错相位特性的双曲余弦-高斯光束则不可能出现空心结构.对影响变换场强度和相位分布的束结构参数及系统参数进行了分析讨论.     

电磁场递推算法及微纳光学元件中的应用

提出一种电磁场递推算法来分析微纳光学元件体内电磁场的传输.该方法基于Maxwell方程组和电磁场横向的边界条件给出了严格解.以高斯光束在亚波长矩形浮雕光栅体内的传输为例,分析了非匀幅光束在微纳光学元件体内的传输. 关键词： 递推算法 非匀幅光束 微纳光学元件     

厄米-双曲正弦-高斯光束的M2因子

从二阶矩的定义出发,给出了一类新光束--厄光-双曲正弦-高斯(HShG)光束M2因子的解析公式,公式表明HShG光束的M2因子是光束阶数n和参数α的函数.作为本公式的特例,给出了厄光-正弦-高斯(HSiG)双束、双曲正弦-高斯(ShG)光束以及正弦-高斯(SiG)光束M2因子的解析公式.对HShG光束的束腰宽度、远场发散角及M2因子做了数值计算,并对所得结果作了分析.     

厄米-双曲正弦-高斯光束的M2因子

从二阶矩的定义出发,给出了一类新光束———厄光双曲正弦高斯(HShG)光束M2因子的解析公式,公式表明HShG光束的M2因子是光束阶数n和参数α的函数.作为本公式的特例,给出了厄光正弦高斯(HSiG)双束、双曲正弦高斯(ShG)光束以及正弦高斯(SiG)光束M2因子的解析公式.对HShG光束的束腰宽度、远场发散角及M2因子做了数值计算,并对所得结果作了分析. 关键词： 厄米-双曲正弦高斯光束 厄米-正弦-高斯(HSiG)光束 M2因子 二阶矩     

衍射光栅空间滤波成像方法实验研究

为了实现毫秒级分辨力光栅式角位移的测量,从光学角度出发,对光栅的设计、制作形成和空间滤波方法进行实验研究;依据马赫-曾德尔干涉法原理进行多光束全息光栅设计;同时对矩形光栅和制作的多光束干涉全息光栅进行相应的空间滤波成像处理;最后选取平行光和点光源两种光源进行检测,并利用面阵CCD和线阵CCD对光栅的衍射信息进行采集,分别从条纹质量、透过率函数和频谱三个方面对空间滤波成像处理前后的光栅进行检验。结果表明:空间滤波成像处理可以减少光栅中高次谐波的含量,明显改善光栅信号的质量;随着衍射光栅空间频率的增大,光栅的正弦性有效提高。     

双层矩形位相光栅的分束特性

对由两矩形位相光栅构成的双层体积全息光栅的分束特性进行了优化设计，获得了扇出光束数分别为２，３和５，总衍射效率高于８９％，光强分布不均匀性小于５％的分束器。     

高质量全息光栅的制作

全息光栅由感光版记录高斯光束干涉条纹制得 ,干涉条纹的不等宽性降低了光栅品质。制取高质量全息光栅的关键是要用均匀平面波作光源。在分析干涉区内光强分布的基础上 ,给出了制作等周期正弦全息光栅的两种方法 :限制曝光区大小的方法和高斯光束强度均匀化的方法。     

Unified design of wavelength-independent deep-etched fused-silica gratings

We present a unified design of wavelength-independent deep-etched fused-silica gratings as polarizing beam splitters and polarization-independent two-port beam splitters by using the simplified modal method. By defining unified grating parameters as the ratio of incident wavelength to grating period and the ratio of groove depth to grating period, unified grating structures are found to be approximately wavelength-independent, which is based on the modal view of the accumulated phase difference of two excited propagating grating modes. Diffraction efficiencies given by the rigorous coupled-wave analysis (RCWA) verified this unified design at the wavelength of 1064 nm. It should be noted that this unified design of wavelength-independent gratings is an analytic result, which is impossible to be derived with the well-known numerical RCWA. Modal method is powerful and presents a clear physical picture for us to obtain this unified design. Therefore, this unified design can be used as a general guideline for designing deep-etched fused-silica gratings as beam splitters for practical applications from ultraviolet to near infrared.     

一种设计环形汇聚光栅反射镜的新方法

提出了一种利用数学变换来快速设计环形汇聚光栅反射镜的方法.通过分析具体的物理场景,抽象出已有条形汇聚光栅的"线"汇聚特性与所要设计的"点"汇聚特性在数学上对应的变换关系,然后用该数学变换对条形汇聚光栅进行外形上的变换,外形变换后的条形光栅即为可以实现"点"汇聚的环形光栅.用有限元算法对设计的环形汇聚光栅进行仿真,仿真证明采用该方法设计的环形光栅可以很好地实现高反、高汇聚.采用这一方法,设计了直径为29.788μm的环形光栅反射镜,当垂直入射的径向偏振光从设计的环形光栅表面反射回来后将发生汇聚,汇聚焦点位于环形光栅表面10μm处.经计算,反射镜的数值孔径为0.8302,反射率为0.9163,在焦点所在的汇聚面上,汇聚光栅电场分布的半高宽为1.5548μm.     

Zemax软件在取样光栅对设计中的应用

 光束取样光栅(BSG)是一种重要的用于光束取样诊断的衍射光学元件。以2块取样光栅代替单块光栅作为初始光学结构,运用Zemax光学设计软件采用分步优化的方法设计了具有消像差功能的光栅对结构,此方法比采用Matlab语言编程计算的方法消像差更快捷、更灵活,同时可以验证程序计算结果的正确性。设计结果显示：再现的会聚光经2块光栅衍射后在像平面上点列图中的均方根半径仅为0.506μm,单块取样光栅的均方根半径则为7.284μm,说明2块光栅能够做到像差互相矫正,其像质明显好于单块取样光栅。另外,设计出的双光栅光学系统,可进行远场光斑质量检测,为激光束性能的在线诊断提供了行之有效的技术支持。     

Fabrication of freestanding nanoscale gratings on silicon-on-insulator wafer

We report a bottom-up process for the fabrication of freestanding nanoscale gratings on silicon-on-insulator (SOI) wafer. Freestanding membrane devices suffer deflection due to the residual stress of the buried oxide layer of SOI wafer. The deflection will affect the device shape and result in the fracture problem for devices fabricated on thin silicon membrane. The bottom-up process is developed to overcome the fabrication issue for thin silicon membrane gratings. The silicon handle layer is removed through back wafer etching of silicon, where the buried oxide layer acts as an etch stop layer. The grating structures are then defined on thin silicon device layer by electron beam lithography and generated by fast atom beam etching. The grating structures are finally released in vapor HF to form the freestanding nanoscale gratings. The freestanding linear/circular gratings, 1,500-nm period grating with the grating width of 200- and 850-nm period grating with the grating width of 100 nm, are successfully achieved on 260-nm silicon device layer.     

Multistate polarization addressing using a single beam in an azo polymer film

Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in an optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photoactive polymer material. The grating orientation follows the incident light beam's polarization direction. The permanent self-induced surface relief grating can be read out in real time using the same laser beam.     

Anomalous behaviour of long-time increase in diffraction efficiency of photorefractive grating in Ce：BaTiO3 in dark

Anomalous long-time increase of the diffraction efficiency is observed in dark-decay experiments of photorefractive gratings in Ce：BaTiO3. It is deduced that a phase-conjugate beam is induced by the writing beam at acute angle to the ＋c axis of the crystal and it interferes with the other writing beam to form a second grating which is perpendicular to the first grating formed by the interference between two writing beams. The rising behaviour of the diffraction efficiency results from the different decay rates of these two photorefractive gratings. Furthermore, a simplified model of two gratings, both induced by two deep traps, is proposed to account for this phenomenon and the fitting results agree well with the experimental results.     

Optical beam deflection using dynamic volume reflection gratings

We propose a scheme for optical beam deflection using dynamic volume reflection gratings. Since the direction change of the diffracted beam with the recording wavelength is much larger for a reflection grating a passive beam-tilting element may not be required.     

Producing and testing binary amplitude gratings using a self-imaging and double-exposure technique

The influence of illuminating beam aberrations and master grating deviations on the performance of the technique of producing arbitrary opening ratio binary gratings using the self-imaging and double-exposure technique is studied analytically and experimentally. It is shown that due to the shear effect encountered in the direction perpendicular to the grating lines and due to the lateral displacement implemented between the two exposures the technique is sensitive to the first derivative of grating in-plane displacements and to the second derivative of the beam and grating out-of-plane errors.     

Beam splitting, combining, and cross coupling through multiple superimposed volume-index gratings

We investigate the diffraction properties of multiple-superimposed index gratings from a vector synthetic viewpoint using coupled wave analysis with Bragg and non-Bragg readout. The vector synthetic gratings consist of two volume-index gratings with different grating wave vectors, which can be obtained in photorefractive materials, in optical fibers or in Bragg cells with two driving acoustic waves. This structure can realize beam splitting, beam combining, and beam cross coupling, etc. Analytic expressions for the diffraction efficiency as well as the amplitude of the waves involved are obtained. The results are presented and discussed.     

Thermal polarization properties of thick anisotropic diffraction holograms recorded in polymer-dispersed liquid crystals

The diffraction and polarization properties of thick anisotropic holographic gratings recorded in polymer-dispersed liquid crystals are studied experimentally and theoretically. Such gratings are anisotropic and sensitive to temperature variations and also exhibit a strong dependence of the diffraction properties on the incident radiation polarization because of the presence of liquid-crystal molecules. The dependences of the diffraction efficiency and diffracted beam polarization orientation on the diffraction grating temperature and incident beam linear polarization are obtained for the case of Bragg incidence. The same dependences are derived using the known experimental temperature curves of the liquid crystal permittivity. The experimental data are in agreement with the theoretical calculations. The feasibility of controlling the diffraction characteristics of the grating in a wide temperature interval is demonstrated.