Optimized phase quantization for diffractive elements by use of a bias phase

Many applications of diffractive phase elements involve the calculation of a continuous phase profile that is subsequently quantized for fabrication. The quantization process maps the continuous range of phase values to a limited number of discrete steps. We report our observation of the influence of this quantization process on the performance of mode-selecting diffractive elements and show that the quantization process produces significantly better results by use of an optimized bias phase. In principle this process can be employed to a greater or lesser extent in any quantization process.     

Design of cascaded diffractive phase elements for three-dimensional multiwavelength optical interconnects

We propose a novel design method that incorporates multiple-layer relief profiles of diffractive phase elements to implement integrated operations on the incident beams according to their wavelengths. We demonstrate simultaneous wavelength-division demultiplexing, arbitrary (even random) wavelength shuffling or routing, spatial focusing, and other manipulations of multiwavelength beams, such as irradiance profile shaping, with design examples for applications in three-dimensional optical interconnects.     

Design of novel laser cavity with diffractive phase elements

A new method based on the general theory of amplitude-phase retrieval is proposed for designing the diffractive phase elements (DPEs) used in the laser cavity that can produce the desired mode with the specified shape of beam. Simulation results show that the laser cavity with the designed DPEs can successfully generate uniform square and triangle ring patterns. The loss of these fundamental modes is negligibly small and the separation of adjacent transverse modes is large enough to discriminate the fundamental mode from the higher-order modes.     

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.     

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。     

Iterative algorithm for the design of diffractive phase elements for laser beam shaping

An improved iterative algorithm for designing diffractive phase elements for laser beam shaping in free space is presented. The algorithm begins with the Gerchberg-Saxton approach to obtain a stable solution. This is followed by several new iterations, in which modified constraining functions are imposed in the Fourier domain while the phase distribution of each iteration remains unchanged. For super-Gaussian beam shaping suitable for inertial confinement fusion applications the mean-square errors of the amplitude and the intensity profile of the entire beam fitted to the corresponding parameters of the 12th-power super-Gaussian beam are approximately 0.035 and 9.75x10(-3), respectively. Approximately 97.4% of the incident energy is converged into the desired region.     

Efficient method for evaluation of the diffraction efficiency upper bound of diffractive phase elements

The theoretical diffraction efficiency upper limit of diffractive phase elements (DPE's) with finite apertures is investigated. A successful numerical method of evaluating the efficiency upper bound of DPE's is proposed. The method includes a hybrid optimization procedure that combines a genetic algorithm with the conjugate gradient method. This efficient global optimization technique can also be used to design DPE's. Simulation computations are detailed for rotationally symmetric beam shaping in which a Gaussian profile laser beam is converted into a uniform beam. Numerical results demonstrate that the estimated diffraction efficiency upper bound is consistent with the design results.     

Precision measurement with visual feedback using binary phase diffractive optical elements

A novel method for obtaining precision measurements by using two binary diffractive optical elements is presented. The system provides visual feedback of the measurement without the use of electronics.     

衍射透镜在多普勒叶尖间隙检测系统中的应用

提出了用折衍混合单透镜代替多普勒叶尖间距检测系统中的双胶合消色差透镜组.对折衍混合单透镜与双胶合消色差透镜的初级像差进行了分析,设计的折衍混合单透镜与双胶合消色差透镜组相比,像差明显减小,光斑位于艾里斑内;光斑半径的均方根达到0.127.从而大大地降低了系统的尺寸和重量,实现了系统的小型化要求.     

Design of near-field irregular diffractive optical elements by use of a multiresolution direct binary search method

A multiresolution direct binary search iterative procedure is used to design small dielectric irregular diffractive optical elements that have subwavelength features and achieve near-field focusing below the diffraction limit. Designs with a single focus or with two foci, depending on wavelength or polarization, illustrate the possible functionalities available from the large number of degrees of freedom. These examples suggest that the concept of such elements may find applications in near-field lithography, wavelength-division multiplexing, spectral analysis, and polarization beam splitters.     

采用分步迭代算法设计制作衍射光学元件

 结合均匀照明相位器件的设计实例，介绍最新提出的基于迭代框架的优化方法，并应用该方法设计制作了16台阶的衍射光学元件并对其进行了测试，验证了设计原理及方法的正确性，且对加工中可能出现的误差进行了分析和讨论。测试结果验证了采用多台阶相位结构的设计方案能有效提高工艺宽容度。     

一种通用的辐射聚焦器设计方法

本文把辐射聚焦器设计当作逆衍射问题求解，在吸收“模拟退火”思想的基础上，提出了一种通用性强、抗局部极值性好的优化算法──Ｉｍｐｒｏｖｅｄ－ＡＬＯＰＥＸ法，并就如何控制优化过程中的温度与步长两参量，进行了详细的讨论，剔除了ＡＬＯＰＥＸ法中存在的一些问题，最后比较了Ｅｒｒｏｒ－Ｒｅｄｕｃｔｉｏｎ法和本方法的设计结果。     

Laser writing system for fabrication of diffractive optics elements

We report a laser writing system for fabrication of diffractive optical elements with He-Cd laser. The wavelength of the light source is 441.6 nm. The output beam is collimated into parallel light with uniform intensity distribution after passing through the spatial filter with a pinhole of 25μm and the collimating device. A microscopy objective lens with numerical aperture (NA) of 0.65 is used to focus the beam into a small diffraction spot. Any pattern can be written with this system. Experimental results are presented.The written gratings and the phase patterns were verified with a conventional optical microscopy and the Taylor Hobson equipment.     

Analysis of materials selected for multilayer diffractive optical elements

An analysis model to optimize the materials selected for multilayer diffractive elements (MLDOEs) is presented with approximate Cauchy dispersion formula of refractive index and the maximum polychromatic integral diffraction efficiency (PIDE). The analysis model presents that the maximum PIDE of MLDOEs consisting of two materials with large Abbe number difference and small partial dispersion difference can be generated. The scope of application and the relationship between diffraction efficiencies of MLDOEs with different material pairs and different design wavelength pairs are presented and simulated with the analysis model of MLDOEs.     

Formation of helical beams by use of Pancharatnam-Berry phase optical elements

Spiral phase elements with topological charges based on space-variant Pancharatnam-Berry phase optical elements are presented. Such elements can be achieved by use of continuous computer-generated space-variant subwavelength dielectric gratings. We present a theoretical analysis and experimentally demonstrate spiral geometrical phases for infrared radiation at a wavelength of 10.6microm .     

Beam delivery of femtosecond laser radiation by diffractive optical elements

Received: 4 February 1998/Accepted: 22 April 1998     

Chromatic-distortion compensation in splitting and focusing of femtosecond pulses by use of a pair of diffractive optical elements

We propose a simple optical system to compensate for chromatic distortion that occurs during fan-out of femtosecond pulses by diffractive optics. The proposed system comprises a pair of diffractive elements, one for splitting an incoming pulse and the other for focusing the split pulses. With an appropriate separation between the elements, chromatic distortion resulting from the spectral bandwidth of a femtosecond pulse is removed, and an array of focused pulses with the same dimensions can be obtained. The theory has been verified through optical and processing experiments with 100-fs, 800-nm pulses.     

Optimized iterative quantization algorithm for phase-only beam shaping masks

In this work, we present a novel and improved method for designing a quantized phase-only beam shaping mask. The algorithm is based on iteratively quantizing the phase while forcing the phase error to produce energy outside the area of interest.The new approach performs well for binary phase-only masks even when a gray level output distribution is required. While comparing to other well-known methods, the proposed approach was found to have fast, simple and stable numerical convergence with low root mean square error as well as high efficiency and signal to noise ratio.     

衍折射设计用于均匀照明的衍射光学器件

 在工艺上衍射光学元件是通过相位板来实现的,由于其多台阶化产生的不连续性,会对目标光场产生sinc调制,产生高级次衍射斑,损失了15%或者更多能量。通过对设计衍射光学器件的传统的IO迭代算法进行了研究,提出了一种与衍折射相结合的设计方法,在衍射光学器件的部分区域形成一块连续相位区域,减少了相位片台阶化区域的光强和衍射斑的强度。通过逐步变化连续相位对输出光强情况的影响的研究,可以优化相位参数,使入射到输出面的光束保证一定匀滑性的前提下,提高目标光场区域的衍射效率达到90%以上,能够满足均匀照明的要求。     

衍折射设计用于均匀照明的衍射光学器件

在工艺上衍射光学元件是通过相位板来实现的,由于其多台阶化产生的不连续性,会对目标光场产生sinc调制,产生高级次衍射斑,损失了15%或者更多能量。通过对设计衍射光学器件的传统的IO迭代算法进行了研究,提出了一种与衍折射相结合的设计方法,在衍射光学器件的部分区域形成一块连续相位区域,减少了相位片台阶化区域的光强和衍射斑的强度。通过逐步变化连续相位对输出光强情况的影响的研究,可以优化相位参数,使入射到输出面的光束保证一定匀滑性的前提下,提高目标光场区域的衍射效率达到90%以上,能够满足均匀照明的要求。