Off-axis Reflective Optical System Research Articles

Compact off-axis reflective optical system design combining freeform mirror and freeform detector

Minimizing system size and weight without sacrificing the desired imaging performance is a crucial and challenging goal in the design of off-axis optical systems. In this paper, we propose a design concept that combines freeform mirror and freeform detector to achieve more compact off-axis optical systems. Initially, by applying nodal aberration theory, the optimal focal surface shape for off-axis systems is demonstrated to be an off-axis paraboloid or even a freeform surface, rather than the commonly assumed spherical shape. Subsequently, we show the ability of the design concept to reduce off-axis system volume through a design example of a fast and wide-field off-axis three-mirror system. Results indicate that, under the same design parameters and imaging quality, the design with a freeform detector is 80% smaller than that with a flat detector in terms of volume. Finally, the bending capability of the freeform detector presented in this paper is ensured through finite element analysis, and its surface accuracy is achievable based on the current precision level of curved detector fabrication. The proposed design concept holds promise for application in planetary science, where the imaging performance of the instrument is highly required and the size and weight are strictly limited.

Design of Parabolic Off-Axis Reflector Optical System for Large Aperture Single Star Simulators

This study proposes a parabolic off-axis reflective optical system design method to reduce the wave aberration of the optical system of a large aperture single star simulator and improve the optical system’s imaging quality. Firstly, we determined the design indexes of the optical system of the large aperture single star simulator by analyzing the technical indexes of the star sensitizer and the development status of the single star simulator; secondly, the initial structural parameters of the optical system were calculated based on the theory of primary aberration; then, we carried out the design optimization of the optical system, the image quality evaluation, and the tolerance analysis using Zemax software; finally, the study tested the wave aberration of the optical system by using the four-dimensional interferometer and the standard mirror together. The simulation results of the optical system are as follows: in the entire field of view, the aberration of the optical system is far less than 0.002%, the modulation transfer function (MTF) reaches the diffraction limit, and the maximum wave aberration is 0.0324 λ. The experimental results are as follows: the maximum wave aberration of the optical system is 0.0337 λ, which is less than 1/25 λ, and it meets the requirements of the index. The simulation and experimental results show that the optical system of the large aperture single star simulator designed by this method has good imaging quality and a simple system structure.

Design Method of Off-Axis Reflective Optical System for Freeform Surfaces under Manufacturing Constraints

Design Method of Off-Axis Reflective Optical System for Freeform Surfaces under Manufacturing Constraints

Fast Stray Light Performance Evaluation Based on BSDF and Radiative Transfer Theory.

Evaluating the stray light cancellation performance of an optical system is an essential step in the search for superior optical systems. However, the existing evaluation methods, such as the Monte Carlo method and the ray tracing method, suffer from the problems of vast arithmetic and cumbersome processes. In this paper, a method for a rapid stray light performance evaluation model and quantitatively determining high-magnitude stray light outside the field of view are proposed by adopting the radiative transfer theory based on the scattering property of the bidirectional scattering distribution function (BSDF). Under the global coordinates, based on the derivation of the light vector variation relationship in the near-linear system, the specific structural properties of the off-axis reflective optical system, and the specular scattering properties, a fast quantitative evaluation model of the optical system's stray light elimination capability is constructed. A loop nesting procedure was designed based on this model, and its validity was verified by an off-axis reflective optical system. It successfully fitted the point source transmittance (PST) curve in the range of specular radiation reception angles and quantitatively predicted the prominence due to incident stray light outside the field of view. This method does not require multiple software to work in concert and requires only 10-5 orders of magnitude of computing time, which is suitable for the rapid stray light assessment and structural screening of off-axis reflective optical systems with a good symmetry. The method is promising for improving imaging radiation accuracy and developing lightweight space cameras with low stray light effects.

Design of off-axis reflective optical system based on planar linkage mechanism

In this paper, we propose a straightforward and dynamic approach to design unobstructed off-axis reflective image systems using a planar linkage mechanism. Objective: The advantage of this design is that it simplifies the process of modeling and optimizing the optical system. Method: The center of the surface is placed at the hinge point, and its tilt angle and position are determined by the adjacent hinge coordinates, and then the curvature of each reflector is determined by the relationship of the optical power. Result: In order to verify the feasibility and convenience of the method, an off-axis four-mirror free-form system is designed, with field of view of 5° × 5°, and the results of the optimized system show that the MTFs greater than 0.8 at 30 lp /mm.

Automatic initial configuration in off-axis reflective optical system design using combined nodal and Seidel aberration.

Currently, an off-axis reflective optical system is designed always from a coaxial initial system, and good imaging performance depends heavily on the choice of good initial configurations. This paper first establishes an imaging-performance evaluation function of the off-axis initial configuration based on nodal aberration theory and Seidel aberration theory. An automatic optimization method of the off-axis initial configuration using the global simulated annealing algorithm is proposed. Two design examples of off-axis three-mirror reflective optical systems are used to demonstrate the effectiveness and simplicity based on the initial configuration design method. Example 1: a series of optical systems with a large 10∘×3∘ field of view (FOV) is quickly and simply implemented using simple surfaces, and the optical systems exhibit perfect imaging quality. Example 2: starting from the good automatic initial configurations, two larger 20∘×3∘ FOV optical systems with focal lengths of 500 mm and f-numbers of five are designed, resulting in good imaging performance and providing a valuable design reference.

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.

基于自由曲面的大视场离轴反射光学系统设计

基于自由曲面的大视场离轴反射光学系统设计

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.

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.

制冷型自由曲面离轴反射光学系统设计

制冷型自由曲面离轴反射光学系统设计

可调焦离轴三反光学系统的装调

可调焦离轴三反光学系统的装调

离轴反射式光学系统结构随机振动响应与疲劳分析

离轴反射式光学系统结构随机振动响应与疲劳分析

Conceptual Design of the NISS onboard NEXTSat-1

The NISS onboard NEXTSat-1 is being developed by Korea astronomy and space science institute (KASI). For the study of the cosmic star formation history, the NISS performs the imaging spectroscopic observation in the near-infrared range for nearby galaxies, low background regions, star-forming regions and so on. It is designed to cover a wide field of view ( deg) and a wide wavelength range from 0.95 to by using linear variable filters. In order to reduce the thermal noise, the telescope and the infrared sensor are cooled down to 200 K and 80 K, respectively. Evading a stray light outside the field of view and making the most use of limited space, the NISS adopts the off-axis reflective optical system. The primary and the secondary mirrors, the opto-mechanical part and the mechanical structure are designed to be made of aluminum material. It reduces the degradation of optical performance due to a thermal variation. This paper presents the study on the conceptual design of the NISS.

A 5-18 MICRON ARRAY CAMERA FOR HIGH-BACKGROUND ASTRONOMICAL IMAGING

ABSTRACT A new infrared array camera system using a Hughes/SBRC 58 x 62 pixel hybrid Si:Ga array detector has been successfully applied to high background 5 - 18 micron astronomical imaging observations. The off-axis reflective optical system minimizes thermal background loading and produces diffraction-limited images with negligible spatial distortion. The noise equivalent flux density (NEFD) of the camera at 10 microns on the 3.0-meter NASA/Infrared Telescope Facility with broadband (Delta lambda/lambda=0.1) interference filters and 0.26 arcsec pixels is NEFD = 0.01 Jy min-1/2 pixel-1 (1 alpha), and it operates at a frame rate of 30 Hz with no compromise in observational efficiency. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and techniques for successful array imaging in a high-background astronomical application are discussed.