Donglin Xue

Designing LED array for uniform illumination distribution by simulated annealing algorithm

We propose a numerical optimization method designing LED array for achieving a good uniform illumination distribution on target plane. Simulated annealing algorithm is employed to optimize LED array arrangement. Using the method, we optimized three LED arrays with various luminous intensity profiles. In order to exhibit the design freedom of the method, we use some LEDs with different intensity value in the first and third array, respectively. By optimizing, the three arrays all produced highly uniform illumination distribution with the uniformity of 0.12, 0.23 and 0.13, respectively. It indicates our method can design various luminous intensity distribution LED arrays and design array consisting of LEDs with different intensity value. In addition, the method is simple and can optimize the LED array automatically by computer program. To the best of our knowledge, it is first time to use numerical optimization method to design the optimal LED array arrangement for uniform irradiance.

Hybrid-level Fresnel zone plate for diffraction efficiency enhancement

The Fresnel Zone Plate (FZP) is widely used in a variety of applications. However, the most concerning drawback of the FZP is its low diffraction efficiency limited by fabrication capability. The diffraction efficiency of an FZP with a surface-relief profile can reach 100% at a specified diffracted order, however, this is difficult to engineer in a precise manner. In this paper, a hybrid-level FZP (HLFZP) is proposed to maximize the diffraction efficiency under a certain lithography condition. To theoretically verify this enhancement, the diffracted field of the HLFZP is derived by establishing a diffraction model. According to different machining capabilities, the design criteria for the level number distribution on the HLFZP are presented. Simulated results show significant improvement in imaging quality while comparing the diffraction efficiency of the specifically designed 8-4-2 HLFZP to that of the traditional 2-level FZP. Fabrication processes for the 8-4-2 HLFZP are developed, with experimental results indicating that the diffraction efficiency could be improved by 54% using the proposed HLFZP, compared to the traditional 2-level FZP. The root mean square (RMS) of the wavefront error for the 8-4-2 HLFZP is 1/20λ (λ = 632.8 nm), and imaging results are good as the predicted results. It is concluded that the proposed hybrid-level method is also promising for improving the diffraction efficiency of other diffractive optical elements.

Positive dwell time algorithm with minimum equal extra material removal in deterministic optical surfacing technology

In deterministic computer-controlled optical surfacing, accurate dwell time execution by computer numeric control machines is crucial in guaranteeing a high-convergence ratio for the optical surface error. It is necessary to consider the machine dynamics limitations in the numerical dwell time algorithms. In this paper, these constraints on dwell time distribution are analyzed, and a model of the equal extra material removal is established. A positive dwell time algorithm with minimum equal extra material removal is developed. Results of simulations based on deterministic magnetorheological finishing demonstrate the necessity of considering machine dynamics performance and illustrate the validity of the proposed algorithm. Indeed, the algorithm effectively facilitates the determinacy of sub-aperture optical surfacing processes.

Rapid fabrication of a silicon modification layer on silicon carbide substrate.

We develop a kind of magnetorheological (MR) polishing fluid for the fabrication of a silicon modification layer on a silicon carbide substrate based on chemical theory and actual polishing requirements. The effect of abrasive concentration in MR polishing fluid on material removal rate and removal function shape is investigated. We conclude that material removal rate will increase and tends to peak value as the abrasive concentration increases to 0.3 vol. %, and the removal function profile will become steep, which is a disadvantage to surface frequency error removal at the same time. The removal function stability is also studied and the results show that the prepared MR polishing fluid can satisfy actual fabrication requirements. An aspheric reflective mirror of silicon carbide modified by silicon is well polished by combining magnetorheological finishing (MRF) using two types of MR polishing fluid and computer controlled optical surfacing (CCOS) processes. The surface accuracy root mean square (RMS) is improved from 0.087λ(λ=632.8  nm) initially to 0.020λ(λ=632.8  nm) in 5.5 h total and the tool marks resulting from MRF are negligible. The PSD analysis results also shows that the final surface is uniformly polished.

Multi-beam array stitching method based on scanning Hartmann for imaging quality evaluation of large space telescopes

To test large-aperture space optical systems in a simple and highly efficient manner, the scanning Hartmann test (SHT) has been used to measure the sub-aperture wavefront slopes of optical systems by scanning with a collimated beam followed by retrieval of the overall wavefront form. However, the use of such a method contains a crucial flaw in that pointing errors of the translation stage can severely affect the test accuracy. Therefore, a multi-beam stitching method is proposed to correct pointing errors by stitching together data obtained by successive sub-aperture acquisition. In this paper, a test principle and a data processing method are detailed. Simulation results theoretically verify a high precision for the stitching algorithm. Furthermore, a multi-beam array stitching test system (MASTS) is developed and used to successfully test an actual space optical system of ∅800 mm. The MASTS shows a deviation of 1/50 λ (λ = 632.8 nm) root mean square (RMS) from the interferometric results and a repeatability of 1/80 λ RMS, which demonstrates high precision, high repeatability and low sensitivity to air turbulence compared to interferometric measurement. In future engineering applications, the MASTS has great potential to solve the test problems of space optical systems using ultra-large apertures.

Microfabrication by Laser Lithography Combined with Ion Etching

Microstructures can enhance the functionality of surfaces in many ways. For the field of optics, the diffraction of light becomes dominant when the size of microstructures is in the order of the applied wavelength. Such diffraction microstructures are being used in many optical applications such as optical imaging, beam splitting, and light concentration. Recently, there are increasing demands for large-aperture diffraction optical elements. Due to strict requirements on both dimensional accuracy and surface roughness, fabrication of such diffraction Z. Zhang (*) · R. Wang · D. Xue Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun, Jilin, China e-mail: zhangzhiyu@ciomp.ac.cn # Springer Nature Singapore Pte Ltd. 2018 J. Yan (ed.), Micro and Nano Fabrication Technology, Micro/Nano Technologies, https://doi.org/10.1007/978-981-10-6588-0_18-2 1 elements has many unique challenges. In responding to these needs, a highefficiency hybrid technology including laser-scanning lithography combined with argon ion etching was developed. Moreover, the replication process of microstructures from glass substrate to ultrathin polymer membrane was also developed to lower the manufacturing cost for meeting the needs of mass production. The developed technologies could be utilized to fabricate large-aperture diffractive optical elements in a variety of future applications.

Ion beam figuring of highly steep mirrors with a 5-axis hybrid machine tool

Ion beam figuring (IBF) is an advanced and deterministic method for optical mirror surface processing. The removal function of IBF varies with the different incident angles of ion beam. Therefore, for the curved surface especially the highly steep one, the Ion Beam Source (IBS) should be equipped with 5-axis machining capability to remove the material along the normal direction of the mirror surface, so as to ensure the stability of the removal function. Based on the 3-RPS parallel mechanism and two dimensional displacement platform, a new type of 5-axis hybrid machine tool for IBF is presented. With the hybrid machine tool, the figuring process of a highly steep fused silica spherical mirror is introduced. The R/# of the mirror is 0.96 and the aperture is 104mm. The figuring result shows that, PV value of the mirror surface error is converged from 121.1nm to32.3nm, and RMS value 23.6nm to 3.4nm.

Effects of the gap slope on the distribution of removal rate in Belt-MRF

Belt magnetorheological finishing (Belt-MRF) is a promising tool for large-optics processing. However, before using a spot, its shape should be designed and controlled by the polishing gap. Previous research revealed a remarkably nonlinear relationship between the removal function and normal pressure distribution. The pressure is nonlinearly related to the gap geometry, precluding prediction of the removal function given the polishing gap. Here, we used the concepts of gap slope and virtual ribbon to develop a model of removal profiles in Belt-MRF. Between the belt and the workpiece in the main polishing area, a gap which changes linearly along the flow direction was created using a flat-bottom magnet box. The pressure distribution and removal function were calculated. Simulations were consistent with experiments. Different removal functions, consistent with theoretical calculations, were obtained by adjusting the gap slope. This approach allows to predict removal functions in Belt-MRF.

Testing and alignment of freeform based multi-mirror telescopes

Three Mirror Anastigmat (TMA) systems including both on-axis and off-axis configurations have been widely used in space applications. In some designs, to correct for high order aberrations and realize large FOV, freeform surfaces are used to provide more design freedoms. This trend brings challenges to optical manufacturing and testing community. Since testing is critical to make high accurate aspheres and freeform surfaces, the paper addressed Computer Generated Hologram (CGH) design and implement to measure large freeform mirrors. In particular, CGH assisted alignment procedure for TMA telescopes were discussed in detail.

Designing, fabricating, and testing freeform surfaces for space optics

Freeform surfaces provide more design freedoms to imaging system without introducing new types of aberrations, therefore better performance can be expected. In this paper, the design of a four-mirror telescope with freeform surfaces was introduced and issues such as tolerancing , manufacturability were discussed; Based on that, fabrication and testing of freeform surfaces were discussed; Particularly direct CNC generation, deterministic polishing techniques including CCOS, MRF and IBF Polishing were presented in detail. Since testing is critical to make high accurate freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large freeform mirrors. In particular, correction of detector to mirror mapping distortion was discussed in detail. Finally, the full field alignment results were given to show the feasibility of using large freeform surfaces in space optics.