Off-axis Three-mirror Optical System Research Articles

Design Method of Freeform Surface Optical Systems with Low Coupling Position Error Sensitivity.

Freeform off-axis reflective systems are significantly more difficult to align and assemble owing to their asymmetric surface shapes and system structures. In this study, a freeform surface system design method with low coupling position error sensitivity (FCPESM) was proposed. First, we established a mathematical model of a reflective system when it was perturbed by coupling position errors and used the clustering-microelement method to establish the coupling error sensitivity evaluation function. The evaluation function was then applied to the design process of a freeform surface off-axis three-mirror optical system. The results showed that the FCPESM optical design method can significantly relax the assembly tolerance requirements of optical systems on the basis of ensuring image performance. In this study, the reflective system was perturbed by tilt and decenter simultaneously, and the disturbance mechanism of position errors on optical systems was further improved. Through this research, freeform surface systems with both image performance and error sensitivity can be obtained, which makes freeform off-axis reflective systems with better engineering realizability.

Integrated Analysis of Line-Of-Sight Stability of Off-Axis Three-Mirror Optical System

As a space camera works in orbit, the stress rebound caused by gravity inevitably results in the deformation of its optomechanical structure, and the relative position change between different optical components will affect the Line-Of-Sight pointing of the camera. In this paper, the optical sensitivity calculation of a space camera’s Line-Of-Sight pointing is realized based on the optomechanical constraint equations, and the Line-Of-Sight equations are constructed using the second type of response (DRESP2) method to realize an optomechanical integrated analysis of the camera’s Line-Of-Sight stability at the structural finite element solver level. The verification results show that the Line-Of-Sight stability error is 6.38%, meaning that this method can identify the sensitive optical elements of the optical system efficiently and quickly. Thus, the method in this paper has important significance as a reference for the analysis of the Line-Of-Sight stability of complex optical systems.

Off-Axis Three-Mirror Optical System Designs: From Cooke’s Triplet to Remote Sensing and Surveying Instruments

The off-axis three-mirror optical system is derived from the classical Cooke triplet or a derivative of the inverse-telephoto lens. By properly arranging an internal reimaging mechanism or altering the location of the optical stop, one can create different versions of three-mirror optical systems. They include very compact configurations and wide field-of-view imagers. Insights into the optical design process, manufacturing, stray light management, and remote sensing applications are presented.

Desensitization design of large freeform off-axis three-mirror optical system (invited)

Desensitization design of large freeform off-axis three-mirror optical system (invited)

A design of supporting structure for realizing large-field-of-view and high-resolution off-axis three-mirror optical system

A design of supporting structure for realizing large-field-of-view and high-resolution off-axis three-mirror optical system

Design of a free-form off-axis three-mirror optical system with a low f-number based on the same substrate.

In this paper, we design a free-form off-axis three-mirror optical system with a low f-number and compact structure, which can be used as an infrared reflection imager. The initial structure is calculated from the near-axis optical transfer matrix based on third-order aberration theory. Particular constraints are designed to install all mirrors on the same substrate for simultaneous milling, which reduces the processing difficulty and effectively avoids errors caused by component assembly. Zernike free-form surfaces are introduced to correct aberrations. This optical system has a field of view of 5∘×5∘ and an f-number of 1.82; the modulation transfer function of the system is higher than 0.6 at 30 lp/mm. The results of the tolerance assignment of the system were verified by the Monte Carlo method, and the machining tolerance is reasonable and easy to achieve. This design not only improves the optical performance of the system but also enhances the feasibility of manufacturing.

Desensitization Design Method for Freeform TMA Optical Systems Based on Initial Structure Screening

Achieving aberration correction can improve the imaging quality of an optical system, and reducing the error sensitivity of system can improve the realizability of the system. In order to obtain an off-axis three-mirror optical system with high image quality and low error sensitivity, a design method is proposed which obtains the initial structure of the three-mirror anastigmatic (TMA) optical system with low error sensitivity through a nondominated sorting genetic algorithm II (NSGA-II). Combining the comprehensive evaluation function of image quality and error sensitivity, this method iteratively selects multiple freeform surface types to determine the combination with the lowest error sensitivity and obtains the freeform TMA optical system with optimal overall performance. A freeform TMA optical system is designed by the method proposed in this paper, and the error sensitivity of the optical system is analyzed. The results show that the image quality of the freeform optical system is effectively improved and the error sensitivity is effectively reduced with the same error applied, which verifies the correctness and practicality of the method.

A Method to Increase the Field of View of an Imaging Optical System

The Y field of view of an off-axis optical system is generally less than 1°. Scholars usually use a freeform surface to achieve a rectangular field of view imaging. However, it adds to the difficulty of processing, testing, assembling, and adjusting, and at the same time has the drawbacks of high manufacturing costs and long processing cycles. In view of the above problems, this paper presents a computational imaging design method for expanding the Y field of view of an off-axis optical system. This method analyzes the aberration characteristics of the optical system, creates a point spread function model based on the wavefront aberration theory and Zernike polynomials, and processes images using a spatial variation deconvolution algorithm. In this paper, we used this method to simulate an off-axis three-mirror optical system with a focal length of 260 mm, the f-number of 2.5, and a field of view of 8° × 1° and compare the images before and after processing. The results show that the processed images have a clear outline, the overall image quality is improved, the field of view is improved to 8° × 6°, and the modulation transfer function of the entire field of view is above 0.4. The off-axis optical system rectangular field of view imaging is realized without using a freeform surface.

Development of the aluminum substrate reflective film in the off-axis three-mirror optical system

Development of the aluminum substrate reflective film in the off-axis three-mirror optical system

Design of multi-band off-axis three-mirror optical system with common aperture

针对军用光电系统对视场范围、图像质量和系统小型化的迫切需求，根据指标要求设计了一种大口径离轴三反光学系统。采用离轴多反式结构消除系统遮拦，缩减结构尺寸，通过引入复杂面型实现大孔径设计，在保证足够分辨率的同时，增大光学系统的视场角，以获得更加丰富的目标特征，提高了系统的目标探测和识别能力。与透射式结构与折返式结构相比，大幅度减小了光电产品的体积和质量，有效减轻了伺服设计负荷，具备隐蔽性好、光谱覆盖范围广、透过率高、视场兼容性强的特点。设计结果表明：电视光路在120 lp/mm处全视场MTF>0.2，短波红外光路在60 lp/mm处全视场MTF>0.3，中波红外在30 lp/mm处全视场MTF>0.15，网格畸变小于0.5%，满足设计指标要求。

Design method for a reflective optical system with low tilt error sensitivity

The realization of the final performance of the optical system depends not only on the aberration correction of the optical design but more importantly on the control of the position error of the optical element during the construction process. Therefore, reducing the error sensitivity of the optical system is an important part of the optical system design process. In order to obtain an optical system with low error sensitivity, this paper proposes an evaluation function of the tilt error sensitivity of the optical system and establishes a desensitization design method for the optical system. Taking an off-axis three-mirror optical system as an example for desensitization design. By comparing the variation of wave front error (WFE) caused by the tilt error of the optical system before and after the desensitization design, the correctness of the evaluation function and the effectiveness of the desensitization design method of the optical system are proved.

Field Curvature Characteristics and Alignment Method for the Off-Axis Three-Mirror Optical System with Wide Field-of-View

Field Curvature Characteristics and Alignment Method for the Off-Axis Three-Mirror Optical System with Wide Field-of-View

动态目标模拟离轴三反光学系统的设计

动态目标模拟离轴三反光学系统的设计

基于自由曲面的离轴三反光学系统设计方法研究

基于自由曲面的离轴三反光学系统设计方法研究

Initial configuration design method for off-axis reflective optical systems using nodal aberration theory and genetic algorithm

Initial configuration is important for optical system design, especially for systems with high requirements in specifications. The number and complexity of optical surfaces needed in an optical system largely depend on the choice of the initial configuration. It is essential to achieve a good initial configuration with minimum aberrations before using complicated surfaces. We propose an initial configuration design method for off-axis reflective optical systems. With this method, a good initial configuration with conic surfaces can be obtained directly. Nodal aberration theory and matrix method are used to calculate the aberration coefficients for the off-axis reflective optical system. Genetic algorithm is applied to search for the initial configuration with minimum aberrations. The validity of this design method is demonstrated by designing an off-axis three-mirror optical system.

Optical design of common-aperture multispectral and polarization optical imaging system with wide field of view**Project supported by the National Natural Science Foundation of china (Grant No. 61471039).

Multispectral and polarization cameras that can simultaneously acquire the spatial, spectral, and polarization characteristics of an object have considerable potential applications in target detection, biomedical imaging, and remote sensing. In this work, we develop a common-aperture optical system that can capture multispectral and polarization information. An off-axis three-mirror optical system is mounted on the front end of the proposed system and used as a common-aperture telescope in the visible light (400 nm–750 nm) and long-wave infrared (LWIR, ) waveband. The system can maintain a wide field of view (4.5°) and it can demonstrate an enhanced identification ability. The off-axis three-mirror system gets rid of central obscuration while further yielding stable system resolution and energy. Light that has passed through the front-end common-aperture reflection system is divided into the visible light and LWIR waveband by a beamsplitter. The two wavebands then converge on two detectors through two groups of lenses. Our simulation results indicate that the proposed system can obtain clear images in each waveband to meet the diverse imaging requirements.

Initial configuration design of off-axis reflective optical system based on vector aberration theory

The traditional method of designing the initial configuration of off-axis reflective optical system is to first obtain the initial configuration of coaxial reflective optical system, and then achieve the unobscured design with an offset aperture stop or a biased input field, or both. Because the aberration distribution of coaxial reflective optical system is not applicable to the off-axis reflective optical system, the obtained unobscured off-axis reflective optical system has large aberration, and the unobscured design process is complicated. In this paper we present a method of designing an initial configuration of off-axis reflective optical system based on vector aberration theory. With this design method, a good unobscured initial configuration of off-axis reflective optical system can be directly obtained by using an offset aperture stop or a biased input field, or both. Based on the vector aberration theory and gaussian brackets, the third-order aberration coefficient is derived for off-axis reflective optical system. Initial configuration performance is important for optical design, especially for the complicated optical system design. The selection of initial configuration highly affects the final system imaging performance, fabrication difficulty and alignment difficulty. An error function is established to evaluate the performance of off-axis reflective optical system, and it consists of aberration coefficients and other constraints. The genetic algorithm is a highly parallel, random and adaptive global optimization algorithm. To obtain a good initial configuration for the off-axis reflective optical system, the genetic algorithm is used to search for the initial configuration with minimum residual aberration. This method can obtain a good initial configuration of off-axis reflective optical system for further optimization. The benefit of this design method is demonstrated by designing an off-axis three-mirror optical system. For the focal plane array, a long-wave infrared off-axis three-mirror optical system is designed. A good initial configuration is obtained with the proposed method, which achieves the unobscured design by using an offset aperture stop and a biased input field. To improve the performance of initial configuration, the obtained initial configuration is optimized with the optical design software. The designed optical system has good imaging quality. As the mirrors are free from the tilts and decenters, the designed optical system is aligned easily.

轻小型大视场自由曲面离轴光学系统设计

With the increasing development of space technology, space optical system with the characteristics of high-performance, miniaturization has become a new hotspot research in space optical fields. Off-axis three-mirror optical system has the advantage of high quality image, large field of view and high level of lightweight etc., which can better suit the application of miniaturized and low-cost space optical system and has broad application prospects. Based on the Gaussian optics and three-mirror aberration theory, the off-axis three-mirror with freeform surface of tertiary mirror was designed. The focal length was 1 550 mm, field of view was 3.60.45, relative aperture was 1:6.2, degrees of freedom and image quality were increased efficiently by the introduction of freeform surface. The design results show that system has a better performance in effective field of view, modulation transfer function value is above 0.43@111 lp/mm, wave-front error maximum value is 0.049 (=632.8 nm), RMS wave-front error value is 0.034 , maximum grid distortion value is 0.9%, and the imaging quality is complete symmetrical about the tangential plane. The total length of the optical system is less than f'/3.1, the height is less than f'/4.1, and is easily implemented because of the relatively loose tolerance about processing and assembling. The obtained results have a certain reference value for miniaturized space optical system.

自由曲面在制冷型离轴三反光学系统的应用

自由曲面在制冷型离轴三反光学系统的应用

基于传递矩阵的宽视场离轴三反光学系统设计

To the problem that off-axis three-mirror optical system has narrow field and complicating initial structure solving process, a method by using optical transfer matrix to solve initial structure was proposed, the focus length and rear cut-off distance of three-mirror system was deduced, then an initial structure parameter of three-mirror system with aperture stop on secondary mirror was given. High order aspheric surface was used to increase system design variance, and making off-axial optimization design to coaxial system based on optical design software ZEMAX, finally got an off-axis three-mirror optical system with wide rectangle field of view 172, focus length of 1 440 mm, F number of 4.8. The system has three high order aspheric optical elements, it can satisfy the requirement of high resolution and large field, the MTF is more than 0.6 at 50 lp/mm, approaches to the diffraction limitation. The designed result shows that the system can be used in space of imaging system with Timed Delay and Integrated Charge-couple Device(TDI-CCD), can expand the ground coverage of system obviously, and achieves high information retrieval efficiency.