Computer-aided Alignment Research Articles

Design of off-axis aspheric four-mirror non-axial mechanical zoom optical system with large relative aperture.

A large relative aperture is essential to improve the spatial resolution of zoom systems. To overcome the limitations of the existing off-axis reflective mechanical zoom system with a low zoom rate and a small relative aperture, this paper proposes a non-axis movement method for increasing the degrees of freedom. On the basis of nodal aberration theory, passive eccentricity is changed into active eccentricity to achieve wave aberration balance in the multiple structures of the zoom imaging system. An off-axis aspherical four-mirror non-axial mechanical zoom optical system is designed and fabricated. The prototype has been successfully processed and assembled with the help of computer-aided alignment technology. The prototype's F-number is 4 and zoom ratio is 4.57:1. Experimental results verify the feasibility of the proposed method.

Optical centering method for lens assembly based on fiber point diffraction interferometry

Centering error in lens assembly reduces the image quality. We proposed an optical centering method based on fiber point diffraction interferometry (FPDI) in this paper. Two fiber point-light-sources (PLSs) interfere longitudinally. The intersection of the line connecting the two PLSs with an imaging plane occurs where the optical path difference (OPD) is an extremum. The line of these two PLSs defines a virtual reference axis. A lens group can be centered by mounting and adjusting lenses piece by piece between the two PLSs and keeping the OPD extremum point as unchanged as possible in this process. Introducing an auxiliary lens can enhance the sensitivity of this method to centering errors. We centered a lens group and showed the effectiveness of the proposed method. Compared with the autocollimation method, the FPDI method does not need to rotate lens elements and is always effective in testing centering errors. In contrast to the calculation of wavefront aberration in the computer-aided alignment (CAA) method, the FPDI method just determines the centering error through the coordinate offset of the OPD extremum point. It utilizes a reference axis that can be precisely positioned by interferometry. The theoretical assembly accuracy can reach micron and arcsec levels.

Application of torque sensitivity in the alignment of a Cassegrain system.

In order to improve the alignment accuracy of a Cassegrain system, to the best of our knowledge, a novel computer-aided alignment method based on torque sensitivity is proposed. Different from the traditional position sensitivity curve guiding scheme, the accurate position of the secondary mirror is not necessary while the torque sensitivity curve is generated. By establishing the relationship between the torque of the secondary mirror setting screw and the Zernike coefficients of the system, a practical quantitative alignment scheme for the Cassegrain system can be realized. For a two-mirror Cassegrain optical-mechanical system, an alignment scheme based on torque sensitivity is designed. The results show that the wavefront aberrations of three Cassegrain systems reach 0.0479λ,0.0537λ, and 0.0698λ respectively. It proves that the torque sensitivity curves can well guide the real alignment process.

Alignment algorithm of nonsymmetric off-axis reflective astronomical telescopes based on the modified third-order nodal aberration theory.

For pupil-offset off-axis reflective astronomical telescopes with designed tilts and decenters, owing to the absence of symmetry, axial and lateral misalignments exhibit strong coupling. The astigmatic and coma aberration fields of the misaligned optical systems are not only effected by lateral misalignments but also closely related to axial misalignments. However, the traditional misalignment algorithm based on nodal aberration theory (NAT) usually ignore the effect of axial misalignments on the aberration fields of optical systems when constructing calculation models. As a result, the presence of axial misalignments in pupil-offset off-axis telescopes with designed tilts and decenters will invalidate the traditional NAT-based lateral misalignment algorithm, which makes it difficult to be applied to actual computer-aided alignment experiments. In order to solve this issue, on the framework of modified NAT, third-order astigmatic, third-order coma, and third-order spherical net aberration fields of pupil-offset off-axis systems with designed tilts and decenters induced by axial and lateral misalignments are separated from the total aberration fields, and their inherent relations are analytically expressed. On this basis, in order to construct a solution model that can simultaneously and quantitatively calculate the axial and lateral misalignments, a method is proposed to fit the partial derivative coefficient matrix of misalignments according to field dependence of the net aberrations induced by misalignments. The simulation and actual alignment experiments were performed on a real wide-field off-axis three-mirror telescope using the constructed solution model, which proved the feasibility of the proposed method. Simulation experiments show that for different misalignment conditions generated randomly, both axial and lateral misalignments have achieved convergent solution results. In the actual alignment experiment, the average RMS wavefront errors of the nine field of views is corrected from 1.9 λ to 0.12 λ (λ = 632.8nm) through 3-5 iterations.

Computer-aided alignment for large-aperture off-axis three mirrors optical system with artificially random air flow

Computer-aided alignment for large-aperture off-axis three mirrors optical system with artificially random air flow

Efficient misalignment calculation for two-mirror optical systems based on wavefront aberrations in a single field of view

Computer-aided alignment (CAA) is a key technology for improving the assembly efficiency and performance of optical systems. However, because of the coma-free pivot point in two-mirror optical systems (TMOSs), the wavefront aberrations from multiple fields of view (FoVs) are required to compute misalignments, and this is not practical. Therefore, misalignment-caused wavefront aberrations were investigated based on the nodal aberration theory, and an analytical aberration computation model for TMOSs was derived. Based on this, an efficient misalignment calculation method based on single-FoV aberrations that introduces known misalignments was proposed and tested by conducting Monte Carlo simulations using the Hilbert telescope. The results showed that micron-level precision can be achieved for the aberration and misalignment calculation without any measurement noise and that a greater number of introduced misalignments can decrease the effect of measurement noise, thereby verifying the effectiveness of the proposed model and method. The findings of this research will open a new direction in CAA by introducing the misalignment rather than the FoV.

Improvement of a computer-aided alignment algorithm for the nonsymmetric off-axis reflective telescope

Due to complications of the off-axis three-mirror anastigmat (TMA) telescope, each optical element in the off-axis TMA telescope is introduced with theoretical eccentricity and tilt. Moreover, the introduction of freeform surfaces and other optical elements with complex surface features generally causes the initial alignment accuracy of the optical path to be low. A large initial alignment error amplifies the sensitivity of the misalignment calculation accuracy to the measurement error of the Zernike coefficient, resulting in difficulty obtaining convergence results for a computer-aided alignment algorithm. Considering the above issues, the alignment sensitivity of each component in the optical path is analyzed in this. The large conditional number of the sensitivity matrix results in poor algorithm robustness. Thus, an adaptive damping factor least-squares algorithm model is proposed and derived to improve the efficiency of the classical least-squares algorithm. A method for piecewise optimization of the damping factor is also deduced. Experiments based on a 0.6 m off-axis TMA telescope verify the effectiveness of the algorithm. Simulation and integration experiments show that the proposed method can reduce the accuracy requirements of the initial alignment and improve the adaptability of Zernike coefficient measurement noise. The alignment procedure is carried out for three iterations, and the average of the five field-of-view wave aberration values is enhanced from 2.1λ (RMS; λ=632.8nm) to 0.09λ (average). The improved algorithm can solve the large initial alignment error of a nonsymmetrical off-axis reflective optical system with a freeform surface as well as the problem of the low success rate of the misalignment value due to low Zernike coefficient measurement accuracy.

Method for compensation selection of a microlithographic optical system.

Computer-aided alignment is very important for the correction of aberrations due to construction imperfections of microlithographic optical systems. The compensation results mostly depend on the selection of compensators. In this paper, an effective method for compensation selection considering optomechanical constraints is presented. The techniques are based on the linearity of compensators and treat compensator selection as a combinatorial optimization problem with the objective of minimum residual aberrations and compensator adjustment ranges. The method is reliable and offers a better combination of compensators under constraints of optomechanical structure. As an example, the method was applied to a lithographic lens with a numerical aperture (NA) of 0.75. The results show that compensators with minimum objective function value would get minimum residual aberrations and adjustment ranges compared to those with larger objective function values. This method presented in this paper could be a good solution for compensation selection in lithographic lenses and other similar optical systems.

Analysis and Optimization of Image Quality Evaluation Function in Computer-aided Alignment of Precision Optical System

The consistent application of computer-aided alignment technology could surmount aimlessness and significantly shorten the align period of complex optical systems. Wherein, the appropriate system image evaluation function is the primary condition to solve the system misalignment successfully. This paper first establishes the relationship between the amount of misalignment and the system aberration through mathematical modelling and then analyzes the relationship between Zernike coefficient, geometric aberration and system image quality in detail, proposes to construct a system image evaluation system using the idea of Zernike coefficient weighting to solve the problem of numerical instability and imprecision of the solutions caused by the direct selection of Zernike coefficients. Subsequently, the experimental alignment of an infrared optical system was performed using the optical system image quality evaluation method established in this paper. The alignment results showed that the RMS value of the system image quality improved by 24.8% under the same solving algorithm compares to the direct selection of the Zernike coefficient and the weighted Zernike coefficient as the system image quality evaluation function. Therefore, the application of the weighted Zernike coefficient-based optical system image evaluation function proposed in this paper is reasonable, feasible, and effective in the computer-aided alignment process.

Research on Applicability of Sensitivity Table Method in Optical System Alignment

Sensitivity table method (STM), which is a most widely used computer-aided alignment technology in optical system alignment, faces a problem that is how to determine the correctness of the applied object and established sensitivity table. In order to solve the problem, two criteria for applying STM correctly are concluded, one is determining the linearity relation between misalignments and wavefront aberration, the other one is establishing the effective sensitivity table by monitoring its condition number. Two optical systems are tested in this paper, and experimental results show the correctness of the proposed method.

Misalignments Computation of a Two-Mirror Optical System based on Modified Merit Function Regression Method

The computer-aided alignment (CAA) is a key technology to align a precision optical system, which is generally a difficult and laborious work. However, many methods proposed has a weak point in that they cannot calculate the misalignments accurately if there are figure error in mirrors. In order to solve this problem, a new modified merit function regression (MFR) is developed, which can compute the misalignments even if the effect of figure error. Misalignments computation based on the traditional and modified MFR are tested in a typical two-mirror optical system, experimental results shows the correctness of modified MFR and its high calculation accuracy.

Digital Staining of High-Definition Fourier Transform Infrared (FT-IR) Images Using Deep Learning.

Histological stains, such as hematoxylin and eosin (H&E), are routinely used in clinical diagnosis and research. While these labels offer a high degree of specificity, throughput is limited by the need for multiple samples. Traditional histology stains, such as immunohistochemical labels, also rely only on protein expression and cannot quantify small molecules and metabolites that may aid in diagnosis. Finally, chemical stains and dyes permanently alter the tissue, making downstream analysis impossible. Fourier transform infrared (FT-IR) spectroscopic imaging has shown promise for label-free characterization of important tissue phenotypes and can bypass the need for many chemical labels. Fourier transform infrared classification commonly leverages supervised learning, requiring human annotation that is tedious and prone to errors. One alternative is digital staining, which leverages machine learning to map IR spectra to a corresponding chemical stain. This replaces human annotation with computer-aided alignment. Previous work relies on alignment of adjacent serial tissue sections. Since the tissue samples are not identical at the cellular level, this technique cannot be applied to high-definition FT-IR images. In this paper, we demonstrate that cellular-level mapping can be accomplished using identical samples for both FT-IR and chemical labels. In addition, higher-resolution results can be achieved using a deep convolutional neural network that integrates spatial and spectral features.

Novel multiple field of view detection method for the off-axis reflection zoom optical system

In order to study the computer-aided alignment for the off-axis reflective zoom optical system, the wavefront aberration of the off-axis reflective zoom system across the field of view needs to be detected. Obtaining the wavefront aberration across the field of view could improve the accuracy of the computer-aided alignment for the off-axis reflective zoom optical system. Restricted by the current wavefront aberration detection technology, only the wavefront aberration at a field degree of 0 could be detected. To solve this problem, a new method to detect the wavefront aberration of off-axis reflective zoom system across the field of view is proposed. According to the traditional autocollimation interferometry method, we improve the detection method by substituting the scan of standard plane mirror with the deformable mirror, replacing the interferometer with Shark-Hartmann sensor and employing the accurately calibrated laser source array to realize the wavefront aberration detection at multiple field of view simultaneously. The simulation shows that the residual wavefront aberration root-mean-square values after compensating for the deformation mirror in the following 6 fields of view (0, 3), (0, 4.2), (0, 5.5), (0, 7), (0, 9.8), and (0, 14) are 0.00039, 0.00075, 0.00024, 0.00017, 0.00053, and 0.0057, respectively. It shows that the detection method we proposed is suitable for the computer-aided alignment technology for the off-axis reflective zoom system.

Computer-aided alignment method in afocal compressed optical path system

摘要: 为了解决随机成分多、调节灵敏度高的离轴反射式系统的精确装调问题，介绍了干涉测量与计算机优化技术相结合的方法，建立了各元件失调量与初级像差之间的关系，以及元件间的像差相互补偿关系，通过干涉测量采集系统全视场的波前差，反向优化得到各元件的失调量，在波长为632.8 nm时，无焦压缩光路系统全视场平均出射波前优于RMS0.055 ，压缩比误差小于5，实现了无焦压缩光路系统高精度、高效率的装调。 关键词: 遥感 / 计算机辅助装调 / 无焦压缩光路系统 / 灵敏度矩阵

Alignment of a three-mirror anastigmatic telescope using nodal aberration theory.

Most computer-aided alignment methods for optical systems are based on numerical algorithms at present, which omit aberration theory. This paper presents a novel alignment algorithm for three-mirror anastigmatic (TMA) telescopes using Nodal Aberration Theory (NAT). The aberration field decenter vectors and boresight error of misaligned TMA telescopes are derived. Two alignment models based on 3rd and 5th order NAT are established successively and compared in the same alignment example. It is found that the average and the maximum RMS wavefront errors in the whole field of view of 0.3° × 0.15° are 0.063 λ (λ = 1 μm) and 0.068 λ respectively after the 4th alignment action with the 3rd order model, and 0.011 λ and 0.025 λ (nominal values) respectively after the 3rd alignment action with the 5th order model. Monte-Carlo alignment simulations are carried out with the 5th order model. It shows that the 5th order model still has good performance even when the misalignment variables are large (-1 mm≤linear misalignment≤1 mm, -0.1°≤angular misalignment≤0.1°), and multiple iterative alignments are needed when the misalignment variables increase.

多光谱相机计算机辅助装调方法

多光谱相机计算机辅助装调方法

Computer-aided alignment of castings and machining optimization

The presented publication demonstrates an accuracy assessment method for machine tool body casting utilizing an optical scanner and reference model of the machine tool body. The process allows assessing the casting shape accuracy, as well as determining whether the size of the allowances of all work surfaces is sufficient for appropriate machining, corresponding to the construction design. The described method enables dispensing with the arduous manual operation of marking out as well as shortening the time of aligning and fixing the casting body for machining. For the experimental setup, four rotary indexing table castings were investigated according to the method principles. The geometric accuracy of each casting was examined by comparing their scans with the computer-aided design model, and the machining allowances were evaluated to determine casting qualification for machining. The nominal volume of material to be removed was established and subsequently optimized to reduce the volume to be machined. Thus, a rapid method of aligning a casting in a machine tool according to the planned optimized distribution of machining allowances was developed. For the set of measured castings, it was proven that their poor geometric quality precluded the possibility of further machining according to standard marking out instructions. However, by following the presented methodology, it was possible to successfully process the entire set while reducing the overall volume of the material removed by 4.5–9.6%, as compared with nominal values. The obtained results ultimately confirmed that manual marking out could be eliminated from the casting assessment process.

微缩投影系统的计算机辅助装调

To solve the coupling problem between the compensators during the computer-aided alignment of a reduced projection system with primary and secondary mirrors and to select the compensators properly,a computer-aided alignment algorithm based on singular value decomposition of an optical system sensitive matrix was described.An alignment model for the reduced projection system was established,and both of the algorithm and the model were accomplished in the experiment.An aspherical surface figure detected with a null lens was introduced into the CODE V optical model,the analysis of the sensitivity matrix was used to supervise the optimization of the optical system,and the optimized structural parameters were considered as the benchmark of the assembly and positioning of optical and mechanical system.The experiments show that the created system alignment model is closer to the actual alignment process,and efficiently supervises system alignment,solves the coupling problem between the compensators,and accelerates the convergence process.Finally,computer-aided alignment experiment was completed based on a self-developed interferometer with high precision.It shows that the system wavefront error is minished from 46.39 nmRMS to 20.73 nmRMS,which veri-fies the veracity of the algorithm and the alignment model.

光学系统计算机辅助装调的坐标基准过渡方法

In order to realize the engineering application of optical system computer-aided alignment and reach the goal of spatial location error correction for optical elements according to the misalignment by calculation, a method of transition between the misalignment by calculation and alignment quantity of adjusting mechanism is presented. Coordinate transform and least squares optimization algorithm are used to establish the misalignment-alignment quantity relation model. The coordinate datum transform between them are finished. Simulation results show that the accuracy of translational alignment quantity can reach 10-6 millimeter order and the accuracy of angular alignment quantity can reach 0.02 order, which are calculated by self-compiled program according to the method. The accuracy of calculation is much higher than the accuracy needed for optical system computer-aided alignment. In the simulation of alignment, compared with the result of alignment on the basis of misalignment by calculation, the result of the method is much better. For different chucking methods of optical elements and adjusting mechanisms, related parameters of the method can be assigned to meet the requirements of different working conditions. The method provides the reference basis for engineering application of optical system computer-aided alignment.

投影光刻物镜的计算机辅助装调

Computer-aided alignment technology is introduced into the alignment of the lithographic lens and mathematical model is established for strict image quality requirements of lithographic lens. The 4th to 37th terms of fringe zernike polynomials and distortion are selected as corrected objects and 19 structural parameters are selected as compensators. The data of sensitivity matrix and image quality are acquired by combing macros of CODE V with Matlab. Singular value decomposition is proposed to calculate the weighted least-squares compensation amount. The Zernike coefficients or distortion of different field is improved by weight factor. The wavefront root mean square difference is about 0.004 and the average distortion difference is about 1 nm between compensated objective and designed objective. The wavefront aberration and distortion are basically recovered to the design level.