Realization of autofocusing system for laser direct writing on non-planar surfaces

This paper presents an autofocusing system for laser direct writing on non-planar surfaces, including focus error signal detection and focusing control. The focus error signal detection is based on modified confocal techniques, which features easy implementation, independence of the tilt angles of non-planar surfaces, and excellent suppression of common-mode noise or variable system factors. We also present a macro/micro dual-drive mechanism and its synchronous operation for focusing control on non-planar surfaces. Finally, a performance evaluation of the autofocusing system is presented. The uniform line width of 2.1 μm for a pattern on a convex spherical substrate with a curvature radius of 100 mm shows the autofocusing system performs well.