Research on edge control in the process of polishing using ultra precise bonnet on optical elements

High-quality optical elements are very important in modern technology; in particular top-quality aspheric optical elements. The concept of an extremely large ground based telescope is a significant technical challenge particularly for the manufacture of the optical components necessary to realize the very demanding performance. Extremely large ground based telescopes require many high-quality, large-diameter optical elements for their construction. The method of optical polishing, using an ultra precise bonnet, is based upon the use of computer controlled fabrication of an optical surface. A bonnet filled with air is used as a precise polishing tool which is flexible and can adapt itself well to the shape of the part, compared with other polishing methods. As with other polishing techniques the edge quality is a key factor affecting the performance of the optical element. In this paper, the effects of edge performance are analyzed, and three compensating techniques are discussed. It is demonstrated that, good edge control can be achieved by using a special removal function applied to the polishing process. Some experimental results are shown and a consecutive polishing process is described.