Research Of Fabricating Microlens Using Dynamical-gradual Grayscale Digital Lithography

In the field of micro optical elements'fabrication, photography technology experienced the development from mask era to non-mask era. Based on the development of MEMS, non-mask photography technology advanced very fast, and the digital non-mask photography was developed in this background. Digital photography have many advantages such as easy to fabricate, save materials to reduce the cost, high precision, have no overlay deviation and can obtain 3D profile with exposing once. And because it has so many advantages, it has become one of the most popular researches in recent years. In this paper, the fabrication of refractive elements based on digital photography was primarily studied. The research contents and results are as follows: 1. the display feature of DMD (Digital Micromirror Device) was fully studied. Considering the displaying distortion of DMD in a certain condition, a well-performing method of microlens'design was proposed to meet the case. From the results of lots of experiments, the reason of DMD displaying distortion was found to have relation to the minimally distinguishable size of the pattern displayed. The equal phase depth designing method of microlens'fabrication in traditional photography is testified that it performed bad in digital photography. And a new design was proposed to solve the problem. The design is using diameter splitting method, which defined that the microlens diameter was equally split according to the size of DMD pixels, to form the microlens quantified by annulus. 2. A new exposure method for digital photography, grayscale gradual changing method, was proposed. According to experimental results, exposure dose can be accurately controlled by using this method, and optimized profile of microlens can be obtained. The deficiencies of fabricating refractive elements using existed methods were discussed, and necessity of proposing a new method to make up the deficiencies was also discussed. Introduced and analyzed the digital moving mask skill and the digital rotating mask skill, and proposed the grayscale gradual changing method using spirit of the two skills. Listed and discussed three branches of the proposed exposure method, common formula for each branch was generalized. Advantages and disadvantages of each method were discussed. In the polytechnic aspect, the relation between exposure dose and photoresist photosensibility was qualitatively studied, and it helped to adjust the grayscale range for practically making. When doing experiments, the exposure system was modified to making better optical elements. Several CAD products for making digital mask were discussed, and CorelDRAW was selected because of its excellent drawing and displaying features.