High-efficiency 1.5 microm thick optical axis grating and its use for laser beam combining

We demonstrate an optical axis grating (OAG) recorded in a nematic liquid crystal that yields a higher than 80% diffraction efficiency and over 800:1 switching contrast between diffraction orders for a laser beam of a red wavelength in a material layer only 1.5 microm thick. The grating was used for combining two laser beams with high efficiency. These observations prove the feasibility of new generation high-efficiency diffractive optical components, which are most promising for infrared and high-power applications owing to their enhanced transparency and reduced thermal effects in thin material layers.     

偏振敏感材料中具有圆各向异性的偏振全息光栅

在向列相液晶中掺杂质量分数约0.2%的偶氮侧链型聚合物制成偏振敏感材料,使用正交圆偏振光记录了具有圆各向异性的一维偏振全息光栅,用线偏振光探测偏振全息光栅,得到正,负一级衍射光也为线偏振光,且偏振态与探测光和零级偏振态相互正交,可以运用琼斯矩阵理论加以解释.偏振全息光栅可由外加电场控制衍射级的变化,即在外加电场作用下,正、负一级衍射产生了90°的相位差.在频率6.05 Hz、电压2.2 V的外场作用下,衍射级的极值振荡变化.     

非对称偏振分束光栅的矢量衍射优化设计

基于严格耦合波理论分析了一种非对称偏振分束光栅的设计。这种偏振分束光栅分别在1级和0级衍射级次上衍射TE和TM偏振波。介绍了利用遗传算法设计偏振分束光栅的方法,并给出了优化实例。仿真结果表明:在设计波长为1.55时,TE偏振波在1级的衍射效率大于93%,TM偏振波在0级的衍射效率大于99%,此时1级和0级的透射消光比分别达到了9914.1和46841.5。通过对设计结果的分析发现,该偏振分束光栅在设计波长附近100nm的波长范围内都具有较高的消光比(大于100),达到了较好的偏振分束效果。     

Role of propagating modes in a double-groove grating with a +1st-order diffraction angle larger than the substrate-air critical angle

Here we show, analytically and numerically, that in a TiO(2) double-groove grating with two different groove widths per period attached on the SiO(2) substrate, the normally incident light couples to the +1st-order transmission with 96.9% efficiency and with a 50° diffraction angle that is larger than the SiO(2)-air interface critical angle. Modal analysis reveals that three propagating modes for the +1st diffraction order reach the grating back end in phase, while the corresponding propagating modes for the -1st and zeroth orders are added destructively at the grating end. Four optical devices based on this grating characteristic are numerically demonstrated.     

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.     

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。     

Polarizing diffraction-grating triplicators

We report experimental results with a reflective continuous anisotropic polarizing diffraction-grating beam splitter that produces three diffraction orders. The diffraction efficiencies and polarizations of the diffracted orders are controlled through the incoming polarization state and by use of a wave plate with arbitrary orientation located between the grating and a mirror. In particular, we show experimental evidence of a diffraction triplicator-a 100% efficiency diffractive device that generates three orders with equal power.     

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。     

Azodye Gelatin Films for Polarization Holographic Recording

Mordant pure yellow azodye in a matrix of gelatin is proposed as a medium for stable polarization recording. Relatively high values of birefringence are measured (over #x0394;n = 0.02). Polarization diffraction gratings are recorded with two circularly polarized waves and diffraction efficiency of 67#x0025; is achieved at 633 nm. Protected from the humidity, the recording is stable. Long-term radiation by a 633 nm probe beam is harmless as well. Unusual behaviour is observed when acting on the recorded grating alternatively with one of the recording beams. The left circularly polarized beam erases the grating sharply, while the right circularly polarized beam, before erasure, initially increases the diffraction efficiency.This paper was originally presented at the 2001 International Conference (2nd Joint OSJ-SPIE Conference) on Optical Engineering for Sensing and Nanotechnology, ICOSN 2001 which was held June 6-8, 2001 at the Pacifico-Yokohama Conference Center, Yokohama, Japan.     

Polarizing beam splitter of two-layer dielectric rectangular transmission gratings in Littrow mounting

We theoretically investigated the design of polarizing beam splitters (PBS) of two-layer dielectric rectangular transmission gratings in Littrow mounting. The PBS grating is aimed to separate TE and TM polarized waves into two different transmitted orders, i.e. the 0th and −1st orders. The polarization-dependent diffraction process is analyzed by using a simplified modal method. The mode reflection and transmission at the interface of the two layers are illustrated. Design equations are given based on the average mode indices of the even and odd modes inside the grating region, which are verified by using rigorous coupled wave analysis. Moreover, with simulated annealing algorithm, two kinds of two-layer PBS gratings are optimized for operation over the C-band (1520-1570 nm). Compared with the single-layer transmission PBS gratings, such two-layer scheme exhibits a great flexibility of design. The PBSs of two-layer dielectric transmission gratings should be useful for practical applications.     

菌紫质同线偏振全息记录时再现光偏振方向对衍射效率的调制

当用相同偏振方向的物光和参考光在菌紫质薄膜上记录光栅时,再现光的偏振方向会影响其衍射效率.采用琼斯矩阵方法对此进行了理论分析,结果显示,再现光的偏振方向对衍射光的光强产生余弦调制;当再现光的偏振方向平行或垂直于记录光的偏振方向时,衍射光仍为线偏振光,其他情况下衍射光均变成椭圆偏振光.再现光偏振方向对衍射效率峰值的调制为正向余弦调制,对衍射效率稳定值的调制为反向余弦调制(与前者在相位上相差π).加入辅助紫光可抑制光栅的饱和,从而使得再现光偏振对衍射效率稳定值的调制由反向余弦调制变为正向余弦调制,并且提高了衍 关键词： 菌紫质 光致各向异性 衍射效率 琼斯矩阵     

Effect of polarization on efficiency of volume Bragg grating filter

<正>Diffraction efficiency of volume Bragg grating,whose period is in the same order as the incident wavelength, is related to the polarization direction of the incident linear polarized beam.When two linearly polarized recording beams with the same polarization direction are used for recording volume Bragg gratings in a photopolymer with diffusion amplification,the azimuth of polarization of the reconstruction beam influences the diffraction efficiency of the grating.When the probe beam is linearly polarized and oriented orthogonally to the grating vectors,the±1-order diffraction beams are also linearly polarized with polarization direction parallel to that of the probe beam.According to the results,a two-dimensional nonspatial optical filter consisting of the volume Bragg gratings would achieve significantly higher efficiency.     

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.     

Ce:KNSBN晶体衍射特性研究

在非同时读出条件下测量了Ce:KNSNB晶体两波耦合体光栅衍射效率随写入光强比、写入光偏振态和写入光夹角的变化关系,并与同时读出条件下衍射效率变化规律的测量结果进行了比较,发现二者基本一致.利用耦合波理论对实验结果进行了理论分析和拟合,拟合结果和实验数据较好的吻合.     

共振域矩形介质光栅的逆向设计

采用模态法研究了共振域光栅分束器及闪耀光栅等光学器件的设计原理及逆向设计方法,给出了-1级非偏振闪耀光栅的典型设计示例。研究表明,自准直角入射时,光束在光栅内传输将激发产生离散模,通过调节离散模透过光栅传输时的累积相位差,可对衍射光进行调控,实现偏振(非偏振)分束、偏振(非偏振)闪耀等功能。采用严格耦合波法对基于模态法逆向设计的-1级非偏振石英闪耀光栅的几何参数进行验证,计算结果显示两者非常吻合,证明了该方法的正确性。     

部分偏振部分相干光光栅衍射场的偏振特性和角相关研究

为了研究部分偏振部分相干光光栅衍射场的衍射特性.利用部分偏振部分相干光的光束相干-偏振(BCP)矩阵,推导出了部分偏振部分相干光通过任意偏振光栅后,衍射场的偏振度及场中衍射级次角相关的一般解析表达式.以部分偏振的高斯-谢尔模型光束(PGSM)为例,数值分析了偏振光栅TE和TM波的复振幅透过率、入射光束的光学参量对衍射场偏振度和场中各衍射级次的角相关的影响.计算结果表明,部分相干光透过偏振光栅后的其衍射光场是一非均匀、周期变化的部分偏振相干光场;场中对称级次的角相干值对应相等,且随衍射级次序数的增大而缓慢递减至零.     

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.     

偏振控制的Ce:KNSBN类光纤光折变光开关

在Ce:KNSBN光折变类光纤晶体中,用不同偏振的读出光控制衍射光强的大小从而实现光折变光开关的开－关功能.实验结果表明e光读出时的光栅衍射效率是o光读出的310倍,而且衍射效率比不随写入光光强比的变化而变化.与块状晶体做了比较,并用理论进行了分析,在光折变类光纤中的衍射效率比是块状晶体的10倍,光折变类光纤晶体有着更好的光开关性能.     

嵌入式镀膜光栅的数值模拟研究

嵌入式镀膜光栅是将平行四边形的介质膜层,以亚波长量级的周期嵌入波导中.针对该光栅在不同偏振态、不同角度入射下的各级衍射效率问题,本文基于严格耦合波分析理论,对该光栅进行建模与数值分析.结果表明,在TE模入射时,该光栅的一级衍射效率可随膜厚在[0,37％]内变化,其余非零级次的衍射效率低于2％.衍射特性可以满足平视器成像的效率递增要求,同时可以减少能量的损失与杂散成像光线.当入射光束的角度在纵向[45°,70°]、横向[-15°,15°]内变化时,一级衍射效率的变化平稳,可以保持平视器不同视场的成像能量均匀.针对入射光偏振态、光栅材料、嵌入膜层倾角、光栅周期对衍射特性的影响,给出了相应的数值分析,可为波导全息平视器中衍射元件的制作提供理论指导.     

Grazing incidence off-plane lamellar grating as a beam splitter for a 1-Å free electron laser

A beam splitter based on the diffraction grating working in the grazing incidence conical diffraction is proposed for x-ray free-electron laser (XFEL) experiments with coherent beams in plasma and atomic physics. Such a beam splitter can provide undistorted wavefronts, high-power radiation scattering, and split beams with equal intensities, which propagate with delay along different paths to the target chamber of the XFEL end station. Using the PCGrate software based on rigorous electromagnetic theory and developed for the short-wavelength range, it is shown that the plane grating with lamellar groove profile of a certain depth, operating in grazing conical incidence mount (grooves are parallel to the incident beam), separates three beams in the ?1, 0, and +1 orders with close diffraction efficiency. Numerical simulation predicts 23–27% absolute efficiency for 0.1-nm incident radiation in each separated order of a bulk or multilayer grating, taking into account the atomic level roughnesses and interdiffusion. When using a multilayer coating based on Ru/C or Ru/B₄C pairs, the optimum grazing angle providing approximately equal efficiencies is ～1.038° which is four times higher than for the Pt-coated grating. Such optimization of radiation geometry, groove profile shape, and multilayer coating parameters can be performed for various XFEL wavelengths. The proposed grating, in addition to diffraction, technological, and design advantages over the beam splitter based on a set of perfect crystals, can be fabricated and tested using currently available methods.