【作者】 周一帆；

【导师】 李洵； 陈四海；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2013， 博士

【摘要】 由两个球面反射镜组成的Schwarzschild系统具有无三阶球差、慧差、像散,以及无色差的优秀光学特性,广泛应用于天文观测领域。利用近二十年发展起来的微光学领域的知识和MEMS工艺技术,将具有百年历史的Schwarzschild结构微缩成微米尺度的微Schwarzschild物镜系统,就为这个古老的结构赋予了新的生命力,使之适用于对物镜的体积和重量有严格要求的各种应用领域,如活体检测、太空探测、数据读写和存储,以及众多手持式消费电子产品等。本论文设计了适合于MEMS工艺制作的微Schwarzschild物镜系统。通过探究大尺寸、小接触角的微透镜以及大尺寸球面微凹腔的设计与制作工艺,研究了系统主镜和次镜的制作方法。通过对不同系统集成方案的设计和制作研究,成功制备并测试了微Schwarzschild物镜系统的原理样镜。主要研究内容和成果综述如下：在微Schwarzschild物镜系统的设计方面,首先通过对不同结构的双反射镜系统的分析,提出了适合MEMS工艺制作的双反射镜系统结构。然后通过推导消像差的条件,得出了系统几何参数应满足的比例关系。结合实际MEMS工艺条件的限制,提出了系统几何参数的设计范围,并提出了一组适合MEMS工艺制作的最佳系统参数。利用光线追迹软件仿真了该系统的光学性能。验证了其消球差、慧差和像散的特点,并分析了系统参数的容差特性。在主镜的制作方面,首先介绍了制作微透镜的不同方法。选择了适合制作大尺寸、小接触角微透镜的丙酮蒸气回流法作为主镜微透镜的制作方法。然后从数学模型上推导了工艺参数和微透镜冠高、曲率半径的关系。采用不同型号,不同厚度的光刻胶,制作了底面直径范围为80～1000μm,冠高范围约为10～120μm的微透镜。探索了采用丙酮蒸气回流法制作微透镜的实验规律,并将实验值与理论模型结果进行了对比。通过对铝膜反射膜厚度的讨论和镀膜方式的分析,在微透镜表面镀制了一层反射膜将微透镜转变为球面反射镜,完成了主镜的制作。在次镜的制作方面,结合Kuiken提出的扩散受限各向同性腐蚀的数学模型,研究了搅拌方式、腐蚀时间、腐蚀窗口大小等参数对腐蚀速度和腐蚀腔形貌的影响。重点分析了实验结果中出现的非球面腐蚀腔,即腐蚀过程中发生的各向异性情况。将实验结果与Kuiken模型提出的两个腐蚀时间域的理论进行了对比,提出了制作大尺寸球面微凹腔的最佳工艺参数范围。并成功制备了满足设计指标的次镜。在集成方面,针对主镜的集成方法提出了两套悬臂设计方案。采用有限元方法分析了悬臂应力分布情况。采用MEMS工艺技术制作了主镜周围的悬臂；采用激光定位打孔技术制作了垫片和次镜中心的通光孔；采用中间层键合的方法完成了主镜和次镜的对准键合,成功制作了微Schwarzschild物镜系统的原理样件。在测试方面,搭建了用于测试原理样件光学性能的显微镜系统实验平台。实验测试了不同像面位置的光斑形状,从而得出了样品的工作距和数值孔径等光学参数。并与仿真值、设计值进行了对比。采用不同波长的色光作为光源,对系统进行了色差测试。测试结果验证了微Schwarzschild物镜系统无色差的特性。最后针对工艺参数的改进方法,提出了未来工作的方向。更多还原

【Abstract】 The Schwarzschild system, composed by two spherical mirrors, enjoys the excellent optical characteristics of no3rd order spherical aberration, coma, astigmatism and chromatic aberration. It has been widely used in the field of astronomical observations. With the help of micro-optics concept and MEMS technology, the one-century-old Schwarzschild system would be given a new life by miniaturization into micron-scale structure. Hence it is suitable for applications which are critical for the size and weight of the microscope objective, such as in vivo detection, space exploration, data read/write or storage, and various handheld consumer electronics products, etc.This paper designs a micro-Schwarzschild objective fabricated by MEMS technology. The primary mirror and secondary mirror are designed and fabricated with the help of the research on the mirolens with large size and small contact angle, and on the spherical mirocavity fabrication. Different integration schemes are discussed, and then the prototype of micro-Schwarzschild objective is fabricated and tested. The main contents and results are summarized as follows:A micro-Schwarzschild objective design is proposed for MEMS fabrication by the discussion on various two-mirror configurations. Then the geometric parameters are designed by deduction of the aberration and the study of limitations of MEMS technology. The light trace software is used to analyse the optical scheme. The property of excellent aberration performance is confirmed by the ray tracing simulation results. And the tolerace characteristics of the system parameters are analysed.Different microlens fabrication methods are discussed. The method of acetone vapor reflow is chosen for the fabrication of primary mirror with large size and small contact angle. Then the relationship between the process parameters and microlens radius of curvarure and crown height is derived from the mathematical model. Photo resists with different thickness are used to produce microlenses with the range of bottom diameter of80-1000μm and the crown height of about10～120μm.After the study on the thickness of aluminum film and the deposit method, a layer of reflective film is coated on the surface to transform the microlens into micro-mirror. And then the primary mirror is successfully fabricated.Kuiken’s mathematical model on the diffusion limited isotropic etching is introducted for the fabrication of the secondary mirror. The impacts of the agitation method, the etching time, the etching window size and other parameters on the profile of etched cavities are studied. The experimental results are analyzed and compared with Kuiken’s model on the two different time periods. The recommended range of process parameters are then proposed for spherical micro-cavity fabrication. The secondary mirror that fits the design values is successfully fabricated.Two sets of cantilever designs for the integration of the primary mirror are proposed. Cantilever stress distribution is analyzed by the finite element method. The cantilever around the primary mirror is fabricated by the MEMS technology, and the apertures on the secondary mirror and middle gasket are produced by laser positioning drilling. The middle layer alignment bonding is used for the integration of the primary and the secondary mirrors to obtain the prototype of the miro-Schwarzschild objective.A testing miroscope system is built to test the optical performance of the prototype. The spot shapes at different image plane positions are captured by CCD. The working distance and numerical aperture are then deducted by the data, and compared with the simulation results and design values. Light sources with different wavelengths are used to test the system’s chromatic aberration. Test results confirm that the system is not wavelength secletive.Finally the impovement of the process parameters and the directions of future work are pointed out.更多还原