Ultraprecision finishing of micro-aspheric surface by ultrasonic two-axis vibration assisted polishing

Micro-glass lenses for digital cameras and blue laser DVD pick-up devices are generally molded by using micro-aspheric ceramic molds made of tungsten carbides. These molds are finished by micro-polishing using loose abrasives after grinding. Improvement to the accuracy of the molds is necessary, and high numerical aperture (NA) optics with steep angles are required. In order to finish the molds of high NA, an ultrasonic two-axis vibration assisted polishing machine with piezo-electric actuators was proposed and developed. Some micro-aspheric molds made of binderless tungsten carbide were polished, and surface roughness of 8 nm Rz was obtained.