Fabrication of Deep Concave Glass Micro Lens by ELID Grinding

Due to the progress in fiber optics, optical storage systems and portable information devices, fabrication technologies for micro optical components becomes more and more important. The fabrication process of micro optical componets especially deep concave glass micro lens is facing a number of diffculties: (1)Since the diameter of the micro optical component is very small and the depth of the surface is large, the grinding wheel must have even samller diameter. (2)In order to obtain optimum cicumference speed, the rotation speed of the grinding wheel becomes extremely high. In order to overcome those problems, inclined grinding wheel can be used to cut the deep concave surface. This method solves the first problem but still extremely high rotation speed is necessary. The authors present a new resolution to those problems using ELID (ElectroLytic In-process Drssing) grinding method. Using ELID grinding, the grinding wheel is continuously dressed during the machininig process and always kept sharpened. This results in a very high quality surface finish even under low circumference speed. Fabrication example of glass micro concave lens (radius:4.6mm) is carried out with small grinding wheel (diameter 5mm) at relatively low rotation speed of 20,000 rpm, which is equivalent to 300m/min circumference speed. Surface roughness of 40nmp-ν and profile accuracy of approximately 1μm was obtained.