A super-resolution Fresnel zone plate and photon sieve

Realizing a smaller or sharper diffractive center spot is a valuable research aim in soft X-ray focus and other related research applications. Fresnel zone plates (FZP) and photon sieves (PS) are often used to focus the X-rays or other wavelength light at present. Here, we show that combination of a super-resolution phase mask (SPM) and an FZP (or PS) as one diffractive optical element can realize a smaller or sharper diffractive center spot without significantly increasing the fabrication difficulty. All these diffractive phase elements can be applied to beam shaping, mask-less lithography, energy congregation in high power lasers, soft X-rays focus, and any other field that requires a smaller or sharper diffractive center spot.     

Creation of a sharper focus by using a rectified TEMp0 beam

The superresolution technique is usually used in optical imaging for its ability to make the central diffractive spot smaller than the Airy spot. In this paper, we apply the superresolution technique for transforming a symmetrical TEM_p0 Laguerre-Gauss beam into a Gaussian intensity distribution in the plane of a converging lens. The beam shaping is achieved by an annular binary Diffractive Optical Element having a transmittance, alternatively equal to −1 or + 1, modelled on the p light rings of the incident beam. It is observed that the rectified TEM₃₀ beam at focus has a focal volume 170 times smaller than that of a Gaussian beam.     

Hybrid Integration Between Long Focus Microlens Array and IR Detector Array

A special method, named step simulation method, is proposed for fabricating Si microlens array to improve the performance of infrared focal plane array (IR FPA). The focus length of rectangle-based multistep microlens array with element dimension of 40 µm×30 µm is 885.4 µm by the method, which is much longer than the focus length of microlens array fabricated by conventional Fresnel binary optics technique., The large-scale 256×256 element microlens array is hybridintegrated with the PtSi Schottky-barrier IR FPA by optical adhesive. The test results show that diffractive spot size of the microlens is 17 µm×15 µm and the average optical response of the IR FPA is increased by a factor of 2.4.     

Polarization converter for higher-order laser beams using a single binary diffractive optical element as beam splitter

We propose a new approach to generating a pair of initial beams for a polarization converter that operates by summing up two opposite-sign circularly polarized beams. The conjugated pairs of vortex beams matched with laser modes are generated using binary diffractive optical elements (DOEs). The same binary element simultaneously serves two functions: a beam shaper and a beam splitter. Two proposed optical arrangements are compared in terms of alignment complexity and energy efficiency. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted.     

Design of refractive/diffractive hybrid optical elements for beam shaping with large diffraction pattern

Diffractive optics is an important technique for beam shaping with high light efficiency and strong diffraction pattern flexibility. Since the diffraction angle is limited by the unit size of the diffractive optical element(DOE),the size of the required diffraction pattern is always rather small. In this Letter, refractive/diffractive hybrid optical elements(RDHOEs) consisting of a DOE and a lens are used to realize beam shaping for a large diffraction pattern. The lens, as the component of the RDHOEs, can not only be concave but also convex,and the double sampling Fresnel diffraction algorithm is developed for the design of these two types of RDHOEs.The simulation and experimental results provide solid evidence to demonstrate the proposed method with the pure phase spatial light modulator.     

二元光学元件

二元光学元件是一种新型的衍射光学元件,它对光学仪器的小型化、集成化起着很重要的作用。本文介绍了二元光学元件的概况,衍射透镜理论,二元光学元件的制造方法以及发展趋势。     

Z-scan sensitivity enhancement using a binary diffractive optics

We report a theoretical study of the sensitivity enhancement of Z-scan technique, using a simple binary diffractive optical element. The latter is a phase aperture made from a transparent plate that has a circular relief introducing a π phase shift in the central region of the incident beam. We demonstrate that the phase aperture acts like a divergence multiplier allowing the Z-scan sensitivity to be increased by a factor of several hundred. PACS 42.25.Fx     

利用汉克尔变换设计高斯光束整形衍射元件的应用研究

衍射光学元件由于可以实现对高斯光束的整形而被重视,其通常的设计方法为G-S算法,由于使用傅里叶变换运算量大、费时长,将快速汉克尔变换应用到这些算法中可以极大地提高运算速度,节省运算时间,为设计复杂的光束整形元件提供了高效、可行的方法。本文利用该种方法设计针对中心波长为775 nm、光束束腰口径为6 cm的激光器,成功设计了一个具有二阶相位的折衍混合光学元件。仅单独这一片元件,既可在距离其35 m处得到一半径为200μm的圆形平顶光斑,均方根误差D0.021。当抽样值取2~15时,在普通PC机上运行时间仅为20.05 s,大大节省了优化设计时间(整个优化设计过程往往需要几十次甚是上百次这种运算)。同时利用离子刻蚀技术加工了该折衍混合元件,并进行了实际测试,结果与设计值基本相符,整形效果较好。这种单片的整形元件不仅整形效果好,还有利于与激光器的集成,简化系统的调节。     

基于叠层衍射成像的二元光学元件检测研究

本文提出了一种基于叠层衍射成像(ptychography)的二元光学元件的检测方法,该方法可实现对二元光学元件表面微观轮廓的检测以及特征尺寸的标定.相比于传统的二元光学元件检测方法,其使用无透镜成像技术,简化了系统结构并可适用于特殊环境下的检测.该方法可直接通过采集多幅衍射图,利用叠层衍射成像迭代算法可精确地复原大尺寸待测元件的表面微观轮廓,提高大尺寸器件的检测效率.本文模拟仿真了台阶高度与噪声大小对纯相位台阶板复原结果的影响,并在光学实验中选取计算全息板为样品,复原样品的表面微观轮廓信息以及得到台阶高度.以白光干涉仪检测结果为标准,该方法在精度要求不太高的前提下,可获得令人满意的成像质量.     

用串行迭代算法设计具有长焦深功能的衍射光学元件

提出一种串行迭代算法,将它用于控制波前传播进行衍射光学元件设计.用此算法设计出能使半导体激光束聚焦并具有长焦深功能的衍射光学元件.模拟计算结果表明了此设计方法的有效性.该衍射光学元件已用光刻和离子刻蚀技术制备并进行了光学实验研究,取得了与理论设计一致的实验结果.     

Wavelength tunable laser beam shaping

Laser beam shaping by phase-only transformations, often referred to as field mapping, has for a long time been considered wavelength dependent. In this Letter we outline a simple mathematical argument that shows how the problem may be formulated in a wavelength tunable manner, requiring only a minor adjustment in the observation plane. We verify the theoretical prediction by experiment using the example of a Gaussian-to-flattop-beam transformation, and we show that the shaping is valid across a wide range of wavelengths for a single diffractive optical element.     

非制冷长波红外热像仪折衍混合双视场光学系统设计

根据衍射光学元件具有大的负向色散特性,将衍射光学元件应用于红外双视场光学系统中,根据傅里叶光学分析衍射光学元件(DOE)的消色差,列表对比折射透镜与衍射光学透镜的特性,并给出变倍比为4∶1可用作非制冷红外热像仪的光学系统的具体设计实例.系统采用切入式变焦方式,在短焦时切入2片透镜实现宽视场,通过引入二元面和非球面提高了成像质量.设计结果表明:在空间频率11 lp/mm处,短焦距40 mm时,各个视场的MTF值均大于0.6;长焦距160 mm时,各个视场的MTF值均大于0.7,宽视场和窄视场都具有较好的成像质量.     

用于光纤传像束的折-衍混合光学耦接器研究

在光学耦接器设计中引入衍射面，根据衍射光学元件的三级像差理论，分析了衍射面初始结构参量的求解规律，通过理论计算和ZEMAX光学软件的优化，给出工作波长0.4~0.7 μm，焦距27.5 mm，光学长度为64 mm，采用一个衍射面的耦接器设计实例.该耦接器适用于单丝直径16 μm，截面直径为6 mm的光纤传像束.对设计结果的分析表明，折-衍混合耦接器不仅在光学性能方面优于传统的光学耦接器，而且在尺寸和重量上有非常显著的减少.     

连续型平面衍射聚光透镜掩模的制作

针对目前二元光学元件掩模制作工艺过程的诸多不足，对连续型平面衍射聚光透镜掩模的激光直写制作工艺进行了研究。基于基尔霍夫标量衍射理论，采用光线追迹法设计了连续型平面衍射聚光透镜掩模。采用激光直写技术，利用CLWS 300M／C极坐标激光直写设备、S1830光刻胶和MICROPOSIT 351显影液，进行了刻写实验。实验表明，激光能量、预烘烤温度、显影液浓度以及预曝光对掩模微结构的制作均有影响。最后制作了掩模。与二元光学元件掩模的制作工艺相比，该技术具有工艺简单、制作周期短且易于操作的优点。     

Design of optical system for head-mounted micro-display

Assembling one optical imaging system with 0.56″ liquid crystal on silicon (LCOS), we achieved one practical head-mounted micro-display system for civilian applications. The optical system consists of three refractive elements and one binary surface. It has a 32° field of view (FOV), a 10 mm exit pupil diameter, and a 20 mm eye clearance distance. Compared with the traditional optical system, the hybrid refractive/diffractive system has a longer working distance and can be used in higher resolution display with better image quality. Designing results indicate that the introducing of binary element in the system with smaller FOV could improve the image quality dramatically.     

消色散光变图像的二元光学设计与制作方法

提出了一种实现消色散光变图像的二元光学方法.以不同取向的狭缝光阑作为目标物光场,采用迭代傅里叶变换算法计算得到具有定向衍射特性的二元位相结构,并作为光变图像的微结构.面向不同图形结构的光变图像,给出了两种不同的数据方案.利用自行研制的激光直写系统以逐图形方式和矢量化直写工作方式分别光刻不同结构的光变图像,位相结构的线宽为2 μm.实验结果表明,定向衍射二元光学位相结构具有消色散特征,且适合于热压复制工艺,为制造消色散光变图像提供了一种新方法.     

Multibeam second-harmonic generation by spatiotemporal shaping of femtosecond pulses

We present a technique for efficient generation of the second-harmonic signal at several points of a nonlinear crystal simultaneously. Multispot operation is performed by using a diffractive optical element that splits the near-infrared light of a mode-locked Ti:sapphire laser into an arbitrary array of beams that are transformed into an array of foci at the nonlinear crystal. We show that, for pulse temporal durations under 100 fs, spatiotemporal shaping of the pulse is mandatory to overcome chromatic dispersion effects that spread both in space and time the foci showing a reduced peak intensity that prevents nonlinear phenomena. We experimentally demonstrate arbitrary irradiance patterns for the second-harmonic signal consisting of more than 100 spots with a multipass amplifier delivering 28 fs, 0.8 mJ pulses at 1 kHz repetition rate.     

折衍二元光学用金刚石车刀设计

栏光效应是影响折衍元件衍射效率的一个重要因素,栏光效应与加工刀具有着密切的关系。分析刀具圆弧半径与栏光效应的联系、刀具参数与元件加工后的表面粗糙度的关系以及刀具耐用度等要求,设计了加工折衍二元光学元件的金刚石刀具,给出刀具加工里程数计算公式和车削实验结果。实验结果证明:设计的金刚石刀具能够满足折衍二元光学元件的产业化加工要求,刀具耐用度较强化前提高2倍多。     

亚波长衍射微透镜的设计

设计了连续浮雕衍射微透镜和与其等效的二元亚波长衍射微透镜,采用旋转体时域有限差分法对通过计算机辅助设计出的元件进行了严格的矢量分析,给出了各元件在焦平面的场强分布.分析结果表明,本文设计的二元亚波长微透镜对连续浮雕微透镜有很好的等效效果;填充因子的脉冲宽度调制法要优于填充因子的线性近似法;制作相对误差不大时深度误差和宽度误差对微透镜聚光能力的影响不大.     

YG算法设计分数傅里叶变换衍射光学光束整形器件

针对分数傅里叶变换衍射光学光束整形器件,比较了按离散点与按菲涅耳积分计算得到的变换矩阵间的差距,从中分析得出按离散点计算的变换矩阵引入的离散化误差与分数傅里叶变换系统参数的关系.模拟计算结果表明,该离散化误差不能忽略.为了在输出面上得到真实的光强分布,应采用菲涅耳积分计算其变换矩阵.鉴于该变换矩阵非幺正,本文利用YG算法进行了光束整形器件的设计.