Profile Measurement of Micro-aspheric Surface by a Small-scale Measuring Instrument

INTRODUCTION Along with the miniaturization of optical devices such as medical endoscopes and fiber-optic communication systems, micro-aspheric lenses (1 mm in diameter) have become very important parts [1]. Micro-aspheric lenses are necessary for downsizing and higher image quality. Form accuracy of micro-aspheric lenses is required to be better than 100 nm to make the most of those devises. However, the 100 nm form accuracy is very hard to achieve because aspheric surface profiles are complicated. On the other hand, accurate profile measurement of the aspheric surfaces for realizing on-line assessment is a big challenge. Scanning probe measurement systems with a contact stylus are practical and suitable for profile measurement of aspheric surfaces [2]. We have developed a novel measurement system for micro-aspheric profiles that employs a contact stylus [3]. Contact styli are capable of measuring complicated surfaces that have steep slope such as aspheric surfaces as long as the probe spheres at probe tips contact with the measuring objects. However, lateral resolution of measuring instruments that employ contact styli is restricted by the radius of probe sphere. Most of commercial styli do not have high enough resolution to be employed for micro-aspheric surface scanning. In this research, a micro-stylus, which is composed of a micro-glass-ball and a micro-stylus, is fabricated and it is applied to the micro-aspheric profile measurement system.