埋入式光栅双通道特性及其应用研究

利用严格耦合波理论分析了埋入式光栅在45°入射时,垂直和平行于光栅栅线的两个不同观察平面的零级共振反射衍射特性.在垂直于光栅栅线的平面内,TE、TM偏振下零级反射共振波长分别为432 am和420 am,在平行于光栅栅线的平面内,TE、TM偏振下零级反射共振主峰波长分别为623 nm和620 nm,在两个平面内,零级共振衍射光的共振波长差别较大,观察到的衍射光颜色差别明显,定义为双通道特性并用实验进行证明,制作了相应的光变色器件.     

透射型光折变体全息光栅对超短脉冲激光光束衍射的特性

在Kogelnik耦合波理论的基础上,考虑光栅记录介质的色散效应的影响,研究了光折变体全息光栅对不同偏振状态的超短脉冲激光光束衍射的性质,讨论了高斯型入射脉冲激光光束的谱宽与光栅的有效衍射谱宽之比不同时,衍射和透射光束的光谱宽度、时间宽度、波形和衍射效率的变化。结果表明,光栅的有效衍射谱宽受光栅参量及入射条件的影响,对衍射性质的影响很大,且在考虑光栅记录介质的色散效应时减小。当入射脉冲的偏振方向垂直于入射面时,光栅的有效衍射谱宽大于偏振方向平行于入射面的情形,衍射效率在入射脉冲宽度较大时小于偏振方向平行于入射面的情形;谱宽比较大时,衍射光束的时间分布曲线产生展宽和变形,且比偏振方向平行于入射面的情形展宽和变形得更加明显。     

矩形槽光栅矢量模式理论的数值计算

本文根据矩形槽光栅的矢量模式理论进行了数值计算。对于任意入射方向及任意偏振态的入射场，计算了其衍射效率和偏振特性变化，并详细研究了光栅结构参数（周期、槽宽、槽深等）对衍射场的影响。     

涡旋光束在反射中的正交偏振特性研究

本文从角谱理论出发建立了涡旋光束在空气-玻璃界面反射时的傍轴传输模型, 并研究了反射过程中诱导产生的正交偏振效应. 当一水平偏振涡旋光束以不同角度入射时, 反射光束的正交偏振分量呈现出类似于一阶厄米-高斯模式的双峰强度分布, 而水平偏振分量强度分布呈现与入射光束相似的分布, 且只在布儒斯特角附近入射时才现出与正交偏振分量垂直的双峰分布. 对于任意线偏振入射光, 其正交偏振分量的偏振方向不再垂直于入射时的偏振方向, 而是与反射光束的中心波矢垂直, 此时正交偏振分量出现有趣的旋转特性, 其物理原因归结于任意线偏振光入射时所对应的水平与垂直偏振分量的反射系数不同. 最后进行了相关实验验证, 发现实验结果与理论分析符合得较好. 关键词： 正交偏振 涡旋光束 任意线偏振     

一种条形亚波长径向偏振光栅

提出并设计了一种条形亚波长铝金属径向偏振光栅,用电子束直写方法制成,可以将偏振光偏振面的旋转直接转换为光斑的水平移动,通过定位光斑位移实现旋光角的测量.光栅由12000个单元水平排列组成,每个单元宽1μm,中心单元的格栅方向为0°,左右相邻单元的格栅分别按逆时针和顺时针方向依次旋转30″,最终实现±50°旋光角的测量范围.基于琼斯矩阵建立了光栅的理论模型,并运用严格耦合波理论分析了光栅的偏振特性与光栅脊厚、周期、占空比、入射光波长之间的关系,确定了光栅的最优结构.实验与仿真结果表明,光栅TM波的透过率大于80%、整体消光比大于26dB.这一测量模式不受光功率波动的影响,可以构成无机械旋转的新型旋光仪,或不需要旋转图像平移转换的电力光学传感器.     

双折射晶体入射、折射光电场矢量的琼斯描述及界面处菲涅耳方程的修正

为了用琼斯矢量更明确地表示双折射晶体入射光和折射光的偏振状态,利用波法线椭球和物质方程,将入射光和折射光的电场矢量均视为由o振动和e振动两个方向的分量叠加而成,并将之投影到垂直于和平行于入射面的两个方向上。其中,入射光和折射光电场分量之间的关系用菲涅耳方程中的透射系数表示。考虑到e光电场矢量与电位移矢量的差别,对菲涅耳方程进行了一定的修正以满足e光的边界条件。最终给出了入射光和折射光电场矢量的琼斯矢量形式。并通过具体的数值计算说明,菲涅耳方程修正前后e光的透射系数有一定的差别,且e光的电场矢量和电位移矢量之间的分裂不可忽略。     

反射型体全息光栅对超短脉冲激光光束衍射的性质

在光栅记录介质色散效应的影响下,拓展Kogelnik的耦合波理论研究了反射型体全息光栅对偏振方向垂直和平行于入射面的超短脉冲激光光束衍射的性质。结果表明对于记录在LiNbO3光折变晶体中的体全息光栅,在色散效应、光栅参量和入射条件的共同影响下,光栅对偏振方向垂直于入射面的超短脉冲激光光束衍射的光谱带宽大于对偏振方向平行于入射面的超短脉冲激光光束衍射的光谱带宽,在不考虑光栅介质色散效应的影响时,它们都变大。进一步给出了衍射光的光谱带宽及光栅的衍射效率随入射脉冲的光谱带宽与光栅的光谱带宽比值的变化情况。     

Polarization characteristics and magneto-optic diffraction efficiency at oblique light incidence

In a great number of papers that deal with the study of the magneto-optic diffraction (MOD), theoretical analysis and interpretation of experimental data are performed without regard for reflection effects of the incident and diffracted light beams on the entrance and exit surfaces of the transparent film. In consequence the MOD parameters are not connected with the angle of light incidence and the orientation of the incident light polarization plane. In the present work the reflection effects are taken into account. For the Raman-Nat diffraction region the general expressions involving the relationships of diffracted light polarization and intensity with the symmetry of the grating, angle of incidence and polarization of the incident light are obtained. In particular it is shown that even for a symmetrical grating the polarization of the zeroth-order diffracted beam differs from that of the incident light, and the polarization of higher-order beams differs from the orthogonal one providing that the incident light is not s- or p-polarized. A maximum in the angular dependence of diffraction efficiency is predicted being observed experimentally.     

局域体全息光栅的衍射特性

基于三维耦合波理论，研究了两束有限宽度的任意偏振平面波干涉产生的局域体全息光栅的衍射问题。以单位均匀振幅的任意偏振平面波为例，给出了透射波和衍射波振幅的主分量和交叉分量的解析表达式，讨论了记录过程和再现过程中入射的参考光波的偏振角对透射波和衍射波振幅的影响。计算结果表明，记录过程中的偏振角越小，形成的光栅内的耦合越强，衍射效率越高，但光束质量越差；再现过程中不同的偏振角，由于入射波和衍射波的电矢量的不同方向的耦合强弱不同，透射波和衍射波振幅的主分量和交叉分量的振幅变化行为不同。     

半圆形金属光栅的矢量模态理论

采用了Ｈａｎｓｅｎ矢量波函数理论研究半圆形金属光栅的衍射效率问题，该方法适用于任意入射方向，任意偏振态入射场衍射问题的研究，结果表明，当入射光为ｐ或ｓ型偏振光时，其结果与文献（１）的结果相同。     

The region of validity of perturbation theory

We present a study of the region of validity of perturbation theory applied to rough surface scattering. We solve numerically the case of a periodic surface or grating varying in one dimension. For a statistical ensemble of gratings with a sufficiently long period one may obtain a good approximation of rough surface scattering. We use this to test the validity of perturbation theory.

Only the perfect conductor case was considered. We find that as the grazing angle becomes small the perturbation result for the TE (E horizontal) polarization remains valid, while for the TM (E vertical) polarization it breaks down. The results show that the perturbation results should be used carefully when being compared with experimental data at grazing angles.     

纳米ZnO薄膜的反射及偏振特性研究

用电子束蒸发镀膜法制备了纳米ZnO薄膜．通过测量其X射线衍射谱,计算出纳米ZnO颗粒的平均粒径大小为30nm．实验研究了纳米ZnO薄膜的反射和偏振性质,结果表明：当振动方向平行于入射面的线偏振光（简称P光）入射纳米ZnO薄膜时,不存在严格意义上的布儒斯特角,但对于入射角却存在一个临界角β．当入射角小于β时,反射光的振动面随着入射角的增大向左旋转;当入射角大于β时,振动面转而向右旋转;当振动方向垂直于入射面的线偏振光（简称S光）入射纳米ZnO薄膜时,反射光的振动面始终向左旋转．     

Optical computing by a vector holographic memory system

We propose what is to our knowledge a novel holographic memory system that is simultaneously applicable to data storage and optical computing. We introduce a polarization-modulated reference beam into holographic recording. A desired spatial-frequency component of an object beam is recorded as a polarization-modulated grating, and the other component is recorded as an intensity-modulated grating. Since the polarization-modulated grating rotates the polarization axis of the incident light by 90 degrees , it is possible to distinguish the desired spatial-frequency component of the retrieved image. Utilizing this property, we have successfully performed spatial-frequency filtering and frequency-selective matched filtering. The system is capable of a variety of optical computations, depending on the design of the polarization modulation.     

亚波长光栅的偏振闪耀特性

 使用琼斯矩阵的方法推导了连续结构亚波长光栅的衍射方程,给出了光栅衍射效率表达式,对偏振特性与衍射特性进行了研究。发现连续结构亚波长光栅仅存在３个衍射级,总衍射效率为100%,且衍射效率可在衍射级间任意分配,0级的偏振态与入射光的偏振态相同,±1级衍射光偏振态与入射光无关,－1级为左旋圆偏振光,＋1级为右旋圆偏振光。通过设置入射光偏振态与光栅相位延迟等参数,可使光栅具有闪耀特性,据此可用于设计高效偏振光分束器和偏振光开关。     

Narrow-bandwidth tunable bandstop filters with circularly cylindrical self-suspended silicon gratings

A circularly cylindrical self-suspended silicon grating (SSG) is proposed, and its reflectance spectrum is investigated by the rigorous coupled-wave method (RCWM). For TM incident polarization, when the grating period is tuned, numerical results by the RCWM reveal that the circularly cylindrical SSG possesses a tunable narrow reflectance bandwidth property in the optical telecommunication wavelength region. It is also demonstrated that both TM incident polarization and the circular grating cross section are easier to bring narrow reflectance bandwidth, compared with TE incident polarization and square grating cross section. Via a micro-electromechanical systems actuator, the proposed circularly cylindrical SSG is expected to serve as a narrow-bandwidth tunable bandstop filter in micro-optical telecommunication systems.     

Electromagnetic scattering from a two dimensional perfect electromagnetic conductor (PEMC) strip and PEMC strip grating simulated by circular cylinders

Electromagnetic scattering of an incident plane wave from a rectangular strip and strip grating, are presented semi-analytically. The strip and strip grating are simulated by joining parallel perfect electromagnetic conductor (PEMC) circular cylinders and are illuminated by a TM_z incident plane wave. The PEMC medium does not allow electromagnetic energy to enter. An interface of this medium serves as an ideal boundary to the electromagnetic field. The solution is based on the application of the boundary conditions on the surface of each cylinder in terms of its local coordinate system. The technique is used to predict the scattered field pattern of PEMC strip and PEMC strip grating.     

相位光栅分离双波长宽角度光线的理论分析

使用衍射光栅的分色分光方式一般以平行光入射情况为讨论基础,对于非平行光入射的情况讨论较少.本文基于菲涅尔衍射理论和角谱理论,将球面波与平面波的衍射波场联系起来,从而在传播函数中引入角度参量,结合分数泰伯效应的理论基础,推导出双波长宽角度入射光线经相位光栅衍射后的波场分布函数,并对推导出的函数进行数值模拟,得到像面不同位置衍射波场分布.与平行光入射时的标准波场分布相比较,得到宽角度入射时的衍射波场的横向展宽量和偏移量.通过调节光栅台阶的宽度,改变衍射场的展宽和偏移,使各个单一波长的衍射波场宽度小于光栅周期的一半,从而减少双波长光衍射波场的混叠.同时本文给出波场宽度与光栅台阶宽度的变化关系,选取光栅面上多个位置作为台阶宽度的计算点,并对整个光栅的台阶宽度进行曲线拟合,得到可以使双波长宽角度入射光实现良好空间分离的光栅参量.该结果可用于各类宽角度入射光线的光谱分离场合,如双波长成像、液晶显示和液晶投影等.     

亚波长介质偏振分束光栅的衍射特性

 采用严格耦合波理论并结合矩阵LU分解法,分析了亚波长介质光栅的刻槽深度、占空比、入射角、入射波长等参数对TE偏振和TM偏振0级衍射效率的影响。结果表明:在1 550 nm波长处,出现瑞利反常现象。由此提出利用瑞利反常现象设计工作波长为1 550 nm的偏振分束光栅,通过优化设计确定了最佳设计参数,即光栅周期为l0/2,瑞利入射角为30°,刻槽深为0.9l0,占空比为0.5。结果表明,参数优化后的偏振分束光栅可以使TE偏振0级反射波和TM偏振0级透射波同时达到近100%的衍射效率。     

Electric-field-controlled two-dimensional Raman-Nath diffraction from paraelectric potassium lithium tantalate niobate

Electric-field-controlled two-dimensional Raman-Nath diffraction has been realized using a photorefractive diffraction grating. The grating was produced by two-wave coupling (at a wavelength of 632.8 nm) at small incidence angles using a potassium lithium tantalate niobate single crystal. Results for the Raman-Nath diffraction from the g₄₄ grating are presented, in which the externally applied field is perpendicular to both the grating vector and the wave vector of the incident beam. Two pairs of coherent beams were used to record the grating for two-dimensional Raman-Nath diffraction. The wave vector and the polarization of one pair lay in the (x, z) plane, and those of the other pair lay in the (y, z) plane. The influence of the applied electric field was studied, and the results show that the intensity of the Raman-Nath diffraction could be controlled by the direction and intensity of the applied field.     

氟化锂偏振器紫外-真空紫外偏振特性的研究

介绍了一种研究偏振元件偏振特性的方法,利用这一方法研究了氟化锂偏振器紫外-真空紫外偏振特征.一组氟化锂偏振器由对称放置的氟化锂晶片组成,各氟化锂片的入射角为60°.利用真空紫外空心阴极光源和Seya-Namioka型紫外-真空紫外单色仪提供单色辐射,测得两片组、四片组和八片组氟化锂偏振器的消光比,与用菲涅尔公式计算的氟化锂偏振器的偏振度在误差范围内一致.利用氟化锂偏振器产生的偏振辐射,初步研究了铝+氟化镁膜反射率以及全息光栅绝对效率在真空紫外波段的偏振特征.