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。     

基于干涉原理精确对中折衍混合器件的技术研究

在折衍混合光学系统的加工和装配过程中,折、衍器件间的对中精度严重影响混合器件的质量和性能,但是由于衍射器件与传统折射器件的显着差异,传统的对中手段已不再适用,如何简便实现二者的精确对中是混合光学系统实用化过程中亟待解决的问题之一.本文提出利用干涉原理简便地实现衍射器件与折射器件的高精度对中,理论分析和实验结果表明该对中装校方法是有效可行的,可以满足光学系统的对中要求。     

Diffractive lenses for high-power terahertz radiation beams

Techniques for manufacturing silicon binary (two-level) diffractive lenses and polypropylene kinoform diffractive lenses for the terahertz spectrum range are described. The elements are 1 and 0.8 mm thick, respectively. The silicon lens is manufactured in two versions: with no coating and with a parylene C (polyparaxylylene) antireflection coating. Characteristics of the diffractive optical elements are studied in the beam of a pulse-periodic free electron laser at a radiation wavelength of 141 μm and a repetition rate of 5.6MHz. The radiation resistance of the parylene coating, tested on the Novosibirsk free electron laser, was not impaired when the coating was exposed to an average power density of 4 kW cm^?2, the peak power in a 100-picosecond pulse being almost 8 MW cm^?2.     

多层衍射元件的浮雕深度和基底材料的优化分析

在分析单层和多层衍射元件衍射效率的基础上,推导出光学系统中多层衍射元件浮雕深度和基底材料的一般关系式,并对这些变量进行优化,得到阿贝数的值大致在20～80之间,β的合理值在0.25～0.6之间,当2个衍射元件的阿贝数v1＜v2,且差值比较大时,阿贝数小的衍射元件的基底材料选择光学玻璃中的火石玻璃,阿贝数大的衍射元件的基底材料选择光学玻璃中的冕牌玻璃。根据这个方法,设计了3组可实现宽波段高衍射效率的不同材料、不同浮雕深度的组合,使得每组组合中两层衍射元件的衍射效率都在99%以上。     

多色光大空间带宽积傅立叶变换透镜系统的设计

本文根据傅立叶变换透镜系统的像差要求，通过研究衍射器件的色差特性和初级像差特点，提出了多色光大空间带宽积的傅立叶变换透镜的系统结构。此系统采用无光焦度的衍射器件校正傅立叶变换主镜的球差，使系统得到最大空间带宽积；还采用谐衍射器件的设计方法，使系统可对多种相干光实现光学傅立叶变换。相对传统傅立叶变换系统而言，此衍射系统结构简单，性能好，可望在光学信息处理方面得到广泛的应用。     

Data preparation and fabrication of DOE using electron-beam lithography

The application of electron-beam lithography to the generation of diffractive optical elements topology is examined. The formula for the estimation of exposure data volume for variable-shaped electron-beam lithography is presented as a function of diffractive optical element parameters and approximation accuracy. A special software dedicated to preparing exposure data for fabrication of diffractive optical elements is developed. Diffractive optical elements with an artificial refractive index are manufactured with a feature size much less than the wavelength. Design and experimental results on photomasks fabrication for an optical element focusing radiation into a ring with pregiven parameters are presented. The photomask set is manufactured for a reflecting optical element focusing the high power CO₂ laser beam into two points with required parameters for laser welding.     

利用二维杨-顾算法设计非对称结构衍射光学元件

杨 顾算法是一种设计衍射光学元件的相位恢复方法。在大多数文献中,主要用它来设计一维衍射光学元件和具有旋转对称结构的二维衍射光学元件,故在此称之为一维杨 顾算法。二维杨 顾算法可用来设计任意结构的二维衍射光学元件。在基于非幺正变换光学系统中,用振幅 相位恢复理论建立了二维杨 顾算法的数学模型,给出了迭代算法。利用自编的仿真程序包设计了一个具有非对称结构的衍射相位元件。     

Diffractive optics: Design, realization, and applications

This paper presents methods for designing and recording optimal computer-generated diffractive optical elements. The design method is based on an analytic ray-tracing procedure for minimizing aberrations. The recording involves computer-generated masks and multiple lithographic processes in order to form reflective and transmissive multilevel, surface relief-phase, diffractive elements. As a result, the elements can have high diffraction efficiencies over a broad range of incidence angles. Even generalized diffractive elements that operate with highly uniform diffraction efficiency and polychromatic radiation can be designed and recorded by optimizing the shape and height of the relief gratings. To illustrate the effectiveness of the diffractive optical elements, they have been incorporated into a number of applications, involving visible as well as infra-red radiation. Some that deal with coordinate transformation, beam shaping, and polarization control are briefly reviewed.     

Pure Diffractive Multicolor Optical Fourier Transform System Design

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衍射光学元件衍射效率的测量

根据衍射光学元件衍射效率的测量原理,建立衍射光学元件衍射效率测量的双光路装置,简要介绍了双光路测量的优点。针对衍射光学元件衍射效率的测量装置,讨论了影响衍射效率测量精度的因素,合理地选择测量装置中的针孔光阑,即可以让主衍射级次的光全部通过被探测器接收,又可以滤掉次级衍射光,保证测量结果的准确度。针对所设计研制的一个折衍射混合成像光学系统,测量了可见光波段3个激光波长的衍射效率,并对测量结果进行了模拟和分析。在473～632.8nm波段范围内任意一个波长处,衍射效率的测量结果同理论值的偏差均小于5.0%。实验证明,双光路测量装置可以用于测量衍射光学元件的衍射效率。     

Making an optical vortex and its copies using a single spatial light modulator

We demonstrate a technique for making copies of optical vortices with the same topological charge using a single spatial light modulator. It has been shown that by using suitable diffractive optical elements, several copies of optical vortices with the same topological charge could be created. We have devised diffractive optical elements using a single spatial light modulator which could be used to make a vortex and its copies without inverting the charge. The nature of the topological charge was investigated with the interferometric technique. The experimental results are verified with the theoretical analysis. We anticipate that our results may find applications ranging from optical manipulation to quantum information.     

Electromagnetic optimization of multilevel diffractive elements by use of the wavelet transform

We present an optimization algorithm for the design of multilevel diffractive optical elements in the electromagnetic domain. The method uses the wavelet transform to parameterize the diffractive optical elements according to a set of coefficients that corresponds to a multiresolution basis. Both local and global optimizations can be performed within a single algorithm. A design example consisting of the optimization of a two-dimensional millimeter-wave diffractive lens over a 10% bandwidth is presented.     

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.     

Investigation of thermo-mechanical behaviour of diffractive optical elements for CO2 lasers

Phase diffractive optical elements are at present proposed for use with infrared high power lasers, for material surface treatment applications. However, the heating of the component exposed to several kilowatts per square centimetre can be a problem for practical implementation. The deformations due to thermal expansion of a gold binary diffraction grating under high power CO₂ laser exposure at 10.6 μm are estimated by a Finite Element Method. They are compared to the geometrical tolerances obtained by a rigorous electromagnetic Fourier modal method which is used to calculate the optical performances. Several exposure parameters (duration, average laser power) and grating parameters (period, line space ratio) are investigated. The laser exposure should be limited to a few milliseconds with a power density on the grating of 10⁴ W/cm², so that the amplitude of the deformations does not exceed the 75 nm tolerance on the grating depth. One is thus assured that the diffraction efficiency in the first order remains superior to 38.5%.     

螺旋光束经过振幅型衍射光学元件的传输特性及其拓扑电荷数的测量

本文提出了一种利用空间光调制器生成杨氏双缝和三角孔等振幅型衍射光学元件的方法. 利用平面波角谱衍射公式和柯林斯公式研究了螺旋光束经过这两种衍射元件后的传输特性, 并利用杨氏双缝和三角孔实现了螺旋光束拓扑电荷数的测量. 由于空间光调制器可以方便和高精度地改变光学器件的几何尺寸和所在的空间位置, 因此可便捷地实现螺旋光束拓扑电荷数的测量.     

Design and fabrication of Fourier plane diffractive optical elements for high-power fibre-coupling applications

In industrial processes using fibre beam delivery of high peak power laser light, diffractive optical elements are a very useful and flexible tool in maximising the amount of light reaching the work surface. This is due to the ability of diffractive optical elements to accurately couple light into multiple fibres, while conditioning the light in order to maximise the throughput for each fibre. We discuss the design techniques for diffractive optical elements and the application of these techniques to fibre-coupling problems. The flexibility of diffractive optical elements is demonstrated by their application to several fibre-coupling geometries, including a fibre bundle, a linear array of fibres, and a rotationally symmetric fibre connector. The diffraction efficiencies for the elements approach 90% with uniformity errors of less than 5%.     

High resolution patterning of sapphire by F<Subscript>2</Subscript>-laser ablation

The ablation behavior of single crystalline sapphire with nanosecond laser pulses at 157 nm wavelength is investigated. Ablation rates of about 10 to 100 nm/pulse are obtained at fluences ranging from 1 to 9 J/cm². At moderate fluences, incubation behavior is observed, i.e. ablation starts after material modification by a number of laser pulses. The ablation can be utilized to fabricate sapphire micro-optics. The capability of creating lenses or gratings on the tip of sapphire fibers is demonstrated. Multilevel diffractive optical elements and high resolution gratings with 1 μm period are fabricated on planar sapphire substrates.     

Volume structuring of high power LED encapsulates by femtosecond laser direct writing

We report on the micro-fabrication of diffractive optical elements (DOEs) such as 1D, 2D and concentric grating structures inside the volume of thin silicone films by femtosecond laser direct writing. In addition, we show that such structures can also be integrated into silicone films that act as encapsulation layers of high power light-emitting diodes. The latter strategy opens new possibilities to homogenize and to control the light emitted from such devices.     

衍射光学元件设计参数对束匀滑衍射效率的影响

经过理论推导,分析了320 mm口径衍射光学元件在束匀滑实验中光强分布出现高级次衍射斑和元件实际衍射效率变低的原因,模拟计算得到了接近实验的光强分布。模拟分析发现:通过调整设计参数,如适当增加抽样点数,使设计时焦斑主瓣占输出计算窗口的比例减小至0.2以下,可以大大降低由于高级次衍射斑造成的衍射效率损失,控制在2%以内,使台阶分布式相位片实际衍射效率得到提高,在对口径为70及320 mm的台阶分布式相位片样品测试中得到了验证。     

Broadband blazing with artificial dielectrics

The efficiency of conventional diffractive optical elements with échelette-type profiles drops rapidly as the illumination wavelength departs from the blaze wavelength. We use high dispersion of artificial materials to synthesize diffractive optical elements that are blazed over a broad spectral range (approximately 1 octave) or for two different wavelengths.