Collinear diffraction of divergent optical beams

Two variants of anisotropic collinear diffraction of light on a sinusoidal diffraction grating are studied theoretically with forth and back light scattering relative to the direction of the incident beam. For both variants, two-dimensional transfer functions are calculated and their modification with optical wavelength and diffraction grating period is analyzed. The dependence of integral diffraction efficiency and filter passband on optical beam divergence is examined.     

SiC/W/Ir multilayer-coated grating for enhanced efficiency in 50-100 nm wavelength range in Seya-Namioka mount

A broadband [SiC/W/Ir](2) multilayer coating was deposited onto a diffraction grating to enhance the grating efficiency in the 50-100 nm wavelength range in a Seya-Namioka mount. The holographic ion-beam etched grating had a laminar profile with 1200 lines/mm. The coating was designed by using the subquarterwave multilayer theory. The measurement results show that the efficiency in the -1st diffraction order is greater than 9.3% throughout the wavelength range of 50-100 nm, which is obviously higher than that of single-layer gratings with SiC, Ir, or Au coatings.     

Measurement of phase differences between the diffracted orders of deep relief gratings

Measurement of the phase difference between the 0th and the 1st transmitted diffraction orders of a symmetrical surface-relief grating recorded on a photoresist film is carried out by replacement of the grating in the same setup with which it was recorded. The measurement does not depend on lateral shifts of thereplaced grating relative to the interference pattern, on environmental phase perturbations or on the wave-front quality of the interfering beams. The experimental data agree rather well with theoretical results calculated for sinusoidal profiled gratings.     

高损伤阈值矩形石英闪耀光栅的设计分析

 采用模态法分析了矩形亚波长石英闪耀光栅的设计原理,给出了1.06 μm工作波长的矩形亚波长石英闪耀光栅的设计示例。研究表明,要设计性能优良的-1级透射闪耀光栅,应使0/1阶传输模的累积相位差为π的奇数倍。设计的透射闪耀光栅能够使TM偏振光和TE偏振光获得近100%的-1级衍射效率,且具有较大的加工容差,较宽的入射波长和入射角变化适应范围。     

单级衍射量子点阵光栅的聚焦离子束直写法制备及光学性能检测

采用聚焦离子束直写技术,成功制作了面积为200μm×200μm,线密度500 mm 1,圆孔直径800 nm,金吸收体厚度为500 nm的单级衍射量子点阵光栅.研究了该光栅在波长442 nm激光下不同传输距离的衍射特性以及相对衍射效率.实验结果表明,量子点阵光栅不存在高级衍射,只保留了±1级和0级衍射,具有良好的单级衍射特性.1级衍射与0级衍射间距随传输距离的增大而增大,实测值与理论计算值相符.     

Polarization-controlled switching between diffraction orders in transverse-periodically aligned nematic liquid crystals

Transverse-periodic-oriented nematic liquid crystals (LCs) are a special type of optical axis grating that are capable of very high efficiency diffraction (theoretically, 100%) in thin layers of materials with thickness comparable to the radiation wavelength. In particular, they fully diffract linearly polarized input beam into circularly polarized +1st and -1st diffraction orders. We experimentally demonstrate switching between diffraction orders of such gratings when the polarization of the incident beam changes from right-circular to left-circular and vice versa with the aid of an electrically controlled LC phase retarder. Such a setup in which the diffraction efficiency and direction are controlled externally, without application of an electric field to the transverse-periodic grating, provides additional control opportunities and does not compromise the quality of the grating. The grating used in the experiment was 1.5 microm thick and had a period of 4 microm. The contrast ratio of switching between the +1st and -1st orders was as high as 267:1 for a He-Ne laser beam with a switching time of 6.6 ms.     

Fabrication and efficiency measurement of a multilayer-coated ion-beam-etched laminar grating for extreme ultraviolet region

We fabricate and measure a multilayer-coated ion-beam-etched laminar grating for the extreme ultraviolet wavelength region. The fabrication process is carefully controlled so that the grating groove and multilayercoating parameters well meet the design targets. At an incident angle of 10°, the peak diffraction efficiency of the ＋1st order is 20.6% at 14.56 nm and that of the -1st order is 22.1% at 14.65 nm, both close to the theoretical limits.     

Optical encoder based on Fractional-Talbot effect using two-dimensional phase grating

This work presents an optical encoder that uses a two-dimensional phase grating. Rather than using a four-windowed scanning grating, this design with a special two-dimensional phase index grating generates two sinusoidal signals that are mutually phase-shifted by 180°. Afterwards, two large-areas, specially structured index grating generates the four 90° electrically phase-shifted scanning signals. The special design of the two-dimensional phase index grating provides more accuracy of phase-shift by using the fact that the  + 1 and −1 diffraction orders are intrinsically phase-shifted from one another by 180°. The gap between the phase index grating and mail scale was increased to three quarters of Talbot distance. The tolerance of gap between the index and main grating is 0.1 mm. The tolerance of yaw motion is ± 0.25°.     

光谱分析方法测试GMLM微间距的实验和方法推广

基于MEMS的光栅平动式光调制器(GMLM)依靠结构中可动光栅和下反射镜之间的微间距的变化来实现光的调制作用,被应用于显示领域。可动光栅和下反射镜之间的微间距是一个关键的参数,传统的测试方法如台阶仪等要破坏结构,WYKO白光干涉仪测量成本高,所以要寻求一种测试成本较低、测量精度较高的测试方法。文章采用非接触的波长扫描式光谱分析方法进行了GMLM可动光栅和下反射镜之间的微间距测试实验研究。实验表明：实验结果和理论分析吻合,验证了理论模型的正确性;对比WYKO白光干涉仪测试,该方法的相对测试误差小于1%;具有很好的重复性。对该光谱分析方法进行了推广,从理论上推导了该方法可以实现准动态测量GMLM器件吸合电压、共振频率以及其他基于衍射/干涉的MEMS器件的微小间距测试等。     

Theoretical reflective performance of a sandwiched two-layer grating polarizer

The reflective polarizer is described by a sandwiched two-layer grating with a metal slab. Such a new polarizer is aimed to improve the performance of a reflective grating-based polarizer. The grating is optimized with the usual duty cycle of 0.5, where TE and TM polarizations are reflected in the –1st and the 0th diffraction orders, respectively. With optimized grating parameters, the extinction ratio can reach 45.5 dB and 41.9 dB in two diffraction orders, which are greatly improved compared with the conventional reported surface grating polarizer with the simple structure. Attractive merits of the new design are high efficiency, high extinction ratio, wide incident wavelength bandwidth for TE polarization, and wide angular range for TM polarization. Numerical results are expected to open new opportunities for the design of a grating-based polarizer with the enhanced performance by the complicated grating configuration.     

基于二维结构薄膜的偏振选择相位光栅的研究

利用二维结构薄膜构建了具有偏振选择特性的新型相位光栅,借助严格耦合波分析(RCWA)方法计算了光栅各级衍射强度随入射光波长及入射角的变化,发现在垂直入射情况下,波长600—640 nm范围内,相位光栅对横向电学(TE)模主要产生0级衍射,而对横向磁学(TM)模产生±1级衍射,在波长633nm处,0级衍射光的偏振消光比为109.8,±1级衍射光的偏振消光比为334.6.利用时域有限差分方法对这种相位光栅的偏振分束现象进行了模拟,偏振分离角在玻璃基板内可以达到10°左右,最后模拟了入射角为23°时光栅对不同偏     

Design of ultrabroadband internal reflection gratings with high efficiency

A high-efficiency, ultrabroadband dielectric internal reflection grating with rhombus-shaped grooves is designed by a rigorous coupled-wave analysis, and an effective method for predicting spectral bandwidths of gratings from their efficiency maps is presented. The grating can be fabricated from a single dielectric material, and its reflection diffraction efficiency of the -1st order can reach more than 0.99. More importantly, an ultrabroadband top-hat diffraction spectrum with efficiency exceeding 0.98 over 170 nm wavelength wide is achieved, which makes the gratings suitable for applications associated with broadband illumination, such as ultrashort pulses.     

Polarizing beam splitter of a deep-etched fused-silica grating

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the -1st and 0th orders, respectively. To achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the -1st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of 1550 nm. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications.     

自支撑透射光栅的设计、制作和测试

采用标量衍射理论和严格耦合波理论分别计算和讨论了金自支撑透射光栅的衍射效率随波长和光栅周期变化的情况并设计了光栅的结构参数.制作了周期为300 nm、线宽/周期比为055、厚度为200 nm、总面积为1 mm×1 mm、有效面积比为65%的金自支撑透射光栅.在国家同步辐射实验室检测了该光栅在55—38 nm波长范围内的绝对衍射效率.检测结果表明所制作的光栅在8 nm附近具有接近10%的最大衍射效率,并且该光栅对于波长15—35 nm范围内的极紫外波段具有基本稳定的衍射效率. 关键词： 自支撑透射光栅 电子束光刻 电镀     

Neutron diffraction by laser-generated volume phase gratings

Cold neutrons are diffracted by thick phase gratings which have been produced by light-optical holography in poly-(methyl methacrylate) (PMMA). The neutron diffraction efficiency is investigated in the Laue case as a function of the angle of incidence by rocking the sample. The dynamical theory of neutron diffraction allows to relate the measured diffraction efficiency to the modulation amplitude of the neutron-optical refractive index. The absence of higher order diffraction peaks proves that this modulation is sinusoidal. Further experimental parameters are shown to influence the diffraction in accordance with the dynamical theory: the wavelength of neutrons, the sample thickness, and the grating period. Laser diffraction experiments allow us to give upper limits for the uniformity of the grating constant throughout the sample volume. The gratings show properties which are promising for the fabrication of high-precision control samples for cold and very cold neutron spectrometers, for the construction of neutron-optical instruments, and the possibility to measure photoinduced changes of neutron-optical potentials.     

提高叠栅条纹信号质量的一种新方法

在国内外普遍使用的细栅距幅光栅叠栅条纹系统中,衍射效应是很明显的,这是造成叠栅条纹信号的衬比(度)和正弦性不好的主要原因.本文在分析了叠栅条纹信号的基础上,导出了衍射光栅副中±1级叠栅条纹的相位与光栅副间隔,光线入射角等的关系,提出了用±1级叠栅条纹来提高叠栅条纹的信号质量,实验结果与理论分析一致,实际应用,效果良好.     

基于光谱合束技术的透射光栅模拟设计

半导体激光器光谱合束技术能够实现近衍射极限的高功率激光输出,已成为当前研究热点。衍射光栅的性能直接决定光谱合束的激光输出效果。模拟设计了一种针对940 nm波长、熔融石英材料的亚波长透射光栅。基于严格耦合波理论对光栅结构进行初步设计,运用Rsoft软件依次对光栅占空比、脊高和周期等参数进行优化确定,同时分析了各个参数对光栅衍射效率的影响。所设计的透射式光栅实现第-1级衍射级次的波分复用功能,衍射效率达到91.2%(TE模式),同时压缩其他衍射级次,使其衍射效率降到1.2%以下。同时在光栅入射角度59°±3°范围内保持90%以上的衍射效率,实现高功率激光输出的同时具有较高的误差容错率,易于调节,满足光谱合束技术的要求。     

1000线/毫米软X射线自支撑闪耀透射光栅的设计与制作

基于标量衍射理论讨论了软X射线自支撑闪耀透射光栅的特性并设计了光栅的结构参数. 采用全息光刻和湿法腐蚀技术, 成功制作了周期1 μm、占空比0.1---0.2、高宽比约100、栅线厚度10 μm、 有效面积比为65%的自支撑闪耀透射光栅. 单元尺寸为15mm× 15mm的硅绝缘体上含有四个5 mm× 5 mm的自支撑闪耀透射光栅窗口. 在国家同步辐射实验室检测了该光栅在5---50 nm波长范围内的衍射效率. 波长扫描测量结果表明, 闪耀效应明显地发生在类似镜面的光栅侧壁镜面反射方向上, 闪耀级次位置及其特征与标量理论预测的一致. 衍射效率的实测结果基本与理论模拟符合, 只是因光栅结构上的缺陷致使衍射效率偏低, 峰值只有理论值的38---49%. 实验结果证明了闪耀透射光栅的概念和湿法制作工艺的可行性.     

Surface plasmon resonance sensor based on diffraction grating with high sensitivity and high resolution

A surface plasmon resonance (SPR) sensor based on diffraction grating with high sensitivity and high resolution is proposed. The sensitivity of grating coupled SPR sensor based on angular interrogation is enhanced by replacing +1st diffraction order of metallic grating with −1st diffraction order to excite the surface plasmon. To improve the resolution of grating-based SPR sensor, aluminum is used as an SPR-active metal. The reflectivity dip of the Al-based sensor is sharper than an Au-based one, which is the mostly widely used as SPR-active metal. And 3-nm-thick gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the sensor not only has high sensitivity and high resolution, but also exhibits good linearity.     

获得高质量Moire条纹信号的一种新方法

在细栅距的幅光栅系统中，衍射效应是很明显的，其能量约占总能量的１０～４０％左右，这种衍射光是造成Ｍｏｉｒｅ光电信号对比度不好和正弦性差的根本原因。本文分析了衍射光栅副±１级Ｍｏｉｒｅ条纹的位相关系与光栅副间隙等因素的关系，提出了利用±１级Ｍｏｉｒｅ条纹来获得高质量Ｍｏｉｒｅ条纹信号，实际应用，效果良好。