用于扩展目标自适应光学校正的相关波前传感器的理论和实验

研究了使用非相干、扩展光源的波前误差测量技术，分析了使用强度透过串型像面掩模的扩展目标相关波前探测原理，讨论了模拟目标的选择问题，探讨了根据目标图像生成像面掩模图像、进而制作像面掩模的方法，给出了所生成的像面掩模图像的典型结果，进行了以强度透过率型掩模为特征的单子孔径扩展目标波前传感器原理实验，比较了两种不同掩模的波前探测效果，获得了与理论分析一致的实验结果。     

用振幅-相位型全息透镜实现光学变换的一般理论

本文将文献[1]和[2]中所讨论的纯相位型的全息透镜系统实现光学变换的理论推广到更普遍情形,提出了用振幅-相位型全息透镜组所构成的光学系统实现给定线性变换的一般理论,推导出诸全息透镜的振幅和相位分布所满足的方程组,应用计算机迭代求解法,不难得到它们的解。     

Zernike-basis expansion of the fractional and radial Hilbert phase masks

The linear Hilbert phase mask or transform has found applications in image processing and spectroscopy. An optical version of the fractional Hilbert mask is considered here, comprising an imaging system with a circular, unobscured pupil in which a variable phase delay is introduced into one half of the pupil, split bilaterally.The radial Hilbert phase mask is also used in image processing and to produce optical vortices which have applications in optical tweezers and the detection of exoplanets.We subjected the fractional and radial Hilbert phase masks to Zernike function expansion in order to compute the image plane electromagnetic field distribution using Nijboer-Zernike theory. The Zernike functions form an orthogonal basis on the unit circle. The complex-valued Zernike expansion coefficients for these two phase masks were derived for use in the context of the Extended Nijboer-Zernike (ENZ) theory of image formation. The ENZ approach is of interest in that it allows a greater range of defocus to be dealt with, provides a simple means of taking a finite source size into account and has been adapted to high Numerical Aperture (NA) imaging applications.Our image plane results for the fractional Hilbert mask were verified against a numerical model implemented in the commercial optical design and analysis code, Zemax^®. It was found that the Nijboer-Zernike result converged to the Zemax^® result from below as the number of Zernike terms in the expansion was increased.     

彩色等效灰度掩模制作方法研究

提出了一种利用彩色等效灰度理论设计掩模的新方法——数据库法.通过选取不同RGB值组合成特定颜色,由彩色胶片输出仪输出这些颜色组成的彩色掩模,获得的彩色胶片掩模用来线性调制曝光量,从而实现二元光学元件台阶深度的线性化.给出了理论计算和16阶菲涅耳透镜的实验结果,证明了数据库方法设计掩模的可行性.该方法的提出为灰度扩展提供了新途径.     

可调谐相位板空域频域联合分析

波前编码系统采用在传统光学系统中加入相位板来扩大光学系统的景深而避免传统景深延拓技术的不利影响. 由于相位板的参数不可调, 整个系统的景深延拓扩展率也不能动态可调. 采用两相位板组合的方法可以有效克服这一点. 本文首先从光线差的角度提出了两三次相位板组合下的光线像差分布以及点扩散函数尺寸的具体关系表达式, 直观体现了系统的光线结构, 指出了光线结构和点扩散函数尺寸受两三次相位板的面型和相对位移量的影响. 其次采用稳相法从空间域给出了系统点扩散函数表达式, 依据点扩散函数的振荡性质给出了有效带宽表达式, 提出了点扩散函数在像面的位置会随两相位板面型参数以及相对于光瞳中心的位移量而发生平移. 最后利用菲涅耳积分给出两三次相位板任意面型参数和相对位移组合下的准确光学传递函数. 在得到的调制传递函数中直观体现出了面型参数和相对位移量对调制传递函数和相位传递函数以及有效带宽的影响, 并说明了此系统相位传递函数的非线性性质. 通过空间域与频率域相结合的方法分析验证了传统的两三次相位板组合具有景深可调和带宽可调的性质, 为设计可调谐波前编码系统提供了理论依据.     

An interference-based optical authentication scheme using two phase-only masks with different diffraction distances

A new method to eliminate the security risk of the well-known interference-based optical cryptosystem is proposed. In this method, which is suitable for security authentication application, two phase-only masks are separately placed at different distances from the output plane, where a certification image (public image) can be obtained. To further increase the security and flexibility of this authentication system, we employ one more validation image (secret image), which can be observed at another output plane, for confirming the identity of the user. Only if the two correct masks are properly settled at their positions one could obtain two significant images. Besides, even if the legal users exchange their masks (keys), the authentication process will fail and the authentication results will not reveal any information. Numerical simulations are performed to demonstrate the validity and security of the proposed method.     

基于空间光调制器的非相干数字全息单次曝光研究

菲涅耳非相干相关全息术(Fresnel incoherent correlation holography,FINCH)利用在空间光调制器(spatial light modulator,SLM)上加载双透镜模式对同一物点光分束自相干,并通过改变加载的相位因子得到不同的相移全息图.本系统利用SLM可分区编码调制特性,将FINCH成像中SLM上分三次加载的0°,120°,240°相位双透镜掩模各提取1/3组成一幅复合相移模式加载,并研究了三种相位分布方式对FINCH成像质量的影响.结果表明:三个相位在SLM上分布间隔越大,再现像越清晰.在此基础上,提出了一种新的掩模加载方式,在SLM加载透镜阵列,每一个相位因子对应一个双透镜,具有一个光轴.实验表明,通过这种加载方式,通过SLM后形成的三个相移图能够一次在电荷耦合器上记录,并且三个相移图不重叠,然后通过MATLAB编程计算将不同相移角度的全息图分别提取出来,通过三步相移计算合成一幅包含有物光波的复值全息图,最后通过数值再现算法重建待测样品.此系统可用于对光源相干性较低的实时成像系统,也为微小形变测量、动态物体的观测提供了新方法,为非相干数字全息术的发展提供了新思路.     

Fabrication of seeded substrates for layer transferrable silicon films

The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work,we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate(PMMA) and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable,unlimitedly reusable substrates for the kerfless technology.     

Selective phase masking to reduce material saturation in holographic data storage systems

Emerging networks and applications require enormous data storage. Holographic techniques promise high-capacity storage, given resolution of a few remaining technical issues. In this paper, we propose a technique to overcome one such issue: mitigation of large magnitude peaks in the stored image that cause material saturation resulting in readout errors. We consider the use of ternary data symbols, with modulation in amplitude and phase, and use a phase mask during the encoding stage to reduce the probability of large peaks arising in the stored Fourier domain image. An appropriate mask is selected from a predefined set of pseudo-random masks by computing the Fourier transform of the raw data array as well as the data array multiplied by each mask. The data array or masked array with the lowest Fourier domain peak values is recorded. On readout, the recorded array is multiplied by the mask used during recording to recover the original data array. Simulations are presented that demonstrate the benefit of this approach, and provide insight into the appropriate number of phase masks to use in high capacity holographic data storage systems.     

A New Algorithm for Die-to-Wafer-like Image Mask Inspection in Real Time

The effect of variations in defect printability must be considered in order to correctly evaluate mask defect inspection procedures. Because of nonlinear transfer effects and strong dependence of printability on defect types, it is difficult to define the boundary between real defect and false defect. To overcome this problem we developed a new algorithm for die-to-wafer-like image (D-to-WI) inspection in real time. This inspection method compares the die (wafer image calculated from CAD data) with the wafer-like image (WI) calculated from the mask image detected by the mask inspection system. To precisely calculate WI in real time, we developed a new simulation-based software. Since the phase of a mask inspection image cannot be measured, we introduce some assumptions regarding its phase. Moreover, we introduce some corrections for WI such as adding a DC component and multiplying by a proper value. To calculate the die which realizes the desired image with sufficient accuracy in real time, we also introduce a perturbation approach. We demonstrate numerically the possibility of a new algorithm for D-to-WI inspection. We confirm that this technique of generating WI from a measured mask pattern is well suited for attenuated phase shift masks (PSMs) and Cr binary masks.     

Intelligibility of reverberant noisy speech with ideal binary masking

For a mixture of target speech and noise in anechoic conditions, the ideal binary mask is defined as follows: It selects the time-frequency units where target energy exceeds noise energy by a certain local threshold and cancels the other units. In this study, the definition of the ideal binary mask is extended to reverberant conditions. Given the division between early and late reflections in terms of speech intelligibility, three ideal binary masks can be defined: an ideal binary mask that uses the direct path of the target as the desired signal, an ideal binary mask that uses the direct path and early reflections of the target as the desired signal, and an ideal binary mask that uses the reverberant target as the desired signal. The effects of these ideal binary mask definitions on speech intelligibility are compared across two types of interference: speech shaped noise and concurrent female speech. As suggested by psychoacoustical studies, the ideal binary mask based on the direct path and early reflections of target speech outperforms the other masks as reverberation time increases and produces substantial reductions in terms of speech reception threshold for normal hearing listeners.     

Large scale ordered topographical and chemical nano-features from anodic alumina templates

We have used ordered anodic alumina membranes as masks to create large scale ordered arrays of either holes or chemical islands on silica. Regularly spaced holes were obtained by direct etching of silica/silicon or glass substrates through the membranes used as etching masks. To create an array of chemically functional islands, the membrane is first glued on the substrate using a soft polymer and subsequently the polymer is etched gently though the mask. Finally organo-silane molecules are deposited through the alumina/polymer hybrid mask and the mask is removed chemically leaving nanoislands on the substrate. We anticipate that this technique will be useful in future biological and biomedical applications.     

利用双全息透镜实现光学普遍变换

在一般情形下(傍轴近似或非傍轴情形)和离散取样情形下,应用逐次反馈迭代算法,导出实现任意给定变换的双全息透镜的振幅-相位分布所满足的方程组.以四维自然序的Walsh变换为例子,给出了双全息透镜的振幅-相位分布和相应的逼近“距离”值,结果令人满意,表明本方案是切实可行的。 关键词：     

Optimized phase pupil masks for extended depth of field

By properly designing a phase pupil mask to modulate or encode the optical images and then digitally restoring them, one can greatly extend the depth of field and improve image quality. The original works done by Dowski and Cathey introduce the use of a cubic phase pupil mask to extend the depth of field. The theoretical and experimental researches all verified its effectiveness. In this paper, we suggest the use of an exponential phase pupil mask to extend the depth of field. This phase mask has two variable parameters for designing to control the shape of the mask so as to modulate the wave-front more flexible. We employ an optimization procedure based on the Fisher information metric to obtain the optimum values of the parameters for the exponential and the cubic masks, respectively. A series of performance comparisons between these two optimized phase masks in extending the depth of field are then done. The results show that the exponential phase mask provide slight advantage to the cubic one in several aspects.     

Research on improving the transverse resolution of binary optical element by digital-division-mask technique

We present the digital-division-mask technique for the first time to solve the problem of decline in transverse resolution, which is caused by using digital micro-mirror device (DMD) to make binary optical elements (BOEs). One high-frequency gray-tone mask can be divided into several low-frequency masks by fixed or variable low-frequency period sampling. And the superimposed lithography effect of these low-frequency masks in the spatial or temporal domain is the same as that of the original high-frequency gray-tone mask. The paper firstly analyzes the digital-division-mask technique in theory and describes the feasibility and advantages. Then taking the diffractive surface fabrication of refractive-diffractive hybrid lens as an example, we conclude that the digital-division-mask technique improves the edge sharpness of lithography pattern, and enhances the diffractive efficiency of BOEs by experiment.     

Fabrication of multi-scale structures with multiple X-ray masks and synchrotron hard X-ray irradiations

Synchrotron hard X-ray irradiation can be utilized in lithography processes to manufacture precise structures. Due to the difficulty of precise X-ray mask fabrication in hard X-ray lithography, this X-ray process has been used mainly to fabricate precise microstructures. In this study, a technology is proposed for fabricating novel multi-scale patterns that include submicron-scale structures using hard X-rays. The required X-ray masks for submicron-sized patterning are fabricated by a simple UV lithography process and sidewall metal deposition. Above all, thanks to the high penetration capability of hard X-rays with sub-nanometer wavelengths, it is possible to employ multiple masks to fabricate a variety of patterns. By combining each sub-micron X-ray mask with typical micro-sized X-ray masks, a unique X-ray lithography is performed, and various multi-scale structures are fabricated. The usefulness of the proposed technology is demonstrated by the realization of these structures.     

Correction of a coherent image during KrF excimer laser ablation using a mask projection

Using masks for laser ablation has proven useful in the fabrication of prototypes for the manufacturing of micro-fluidic devices. In this work, an excimer laser was used to engrave microscopic channels on the surface of polyethylene terephthalate (PET), which showed a high absorption ratio for an excimer laser beam with a wavelength of 248 nm. When 50 μm wide rectangular microscopic channels were made using a 500×500 μm square mask and a magnification ratio of 1/10, ditch-shaped defects were found at both corners. The calculation of the laser beam intensity showed that a coherent image in the PET specimen caused the defects. An analysis based on the Fourier diffraction theory enabled the prediction of a coherent shape at the image plane, as well as a diffracted beam between the mask and the image plane. The analysis also showed that the diameter of the aperture was a predominant factor toward the elimination of ditch-shaped defects in the rectangular microscopic channels on the PET produced by an excimer laser ablation.     

Asymmetric multiple-image encryption based on the cascaded fractional Fourier transform

A multiple-image cryptosystem is proposed based on the cascaded fractional Fourier transform. During an encryption procedure, each of the original images is directly separated into two phase masks. A portion of the masks is subsequently modulated into an interim mask, which is encrypted into the ciphertext image; the others are used as the encryption keys. Using phase truncation in the fractional Fourier domain, one can use an asymmetric cryptosystem to produce a real-valued noise-like ciphertext, while a legal user can reconstruct all of the original images using a different group of phase masks. The encryption key is an indivisible part of the corresponding original image and is still useful during decryption. The proposed system has high resistance to various potential attacks, including the chosen-plaintext attack. Numerical simulations also demonstrate the security and feasibility of the proposed scheme.     

Laser-induced ablation of polymers using a patterned dopant generated from a leuco-dye precursor via flood exposure: A “portable conformable mask” approach to laser ablation of PMMA at 351 nm

A two-stage laser ablation process is described, which initially generates a laser-light absorbing image from a conventional photolithographic mask via a UV-flood exposure step. For this purpose a colorless precursor of a dye, i.e., its leuco form, is imbedded into the polymer to be ablated as a dopant. For poly(methyl methacrylate) as such a polymer, triphenylmethanol, the leuco precursor for the corresponding triphenylmethyl dye represents a good choice for ablation with excimer lasers operating at the wavelength 351 nm. In this fashion conventional masks and exposure tools of UV-photolithography may be used in combination with laser ablation. The resulting images are characterized by a good contrast and reasonably sharp contours. The photochemical mechanism and additional aspects of this two-step process, which resembles the “portable conformal mask” approach of photolithography, are outlined.