Flexible fabrication of micro-optics arrays with high-aspect-ratio by an offset-tool-servo diamond machining system

Micro-optics arrays (MOAs) with high aspect ratio (AR) have unique advantages in realizing the minimization of optical systems by reducing the focal distance. Fast or slow tool servo (F/STS) is widely regarded as an outperforming technique for the fabrication of MOAs featuring high form accuracy. However, in the machining of MOAs with high AR, the non-smooth cutting trajectory of F/STS inevitably leads to intensive tool vibrations and the interference between the tool flank face and the finished surface, thereby deteriorating surface roughness. In this study, a novel offset-tool-servo (OTS) diamond machining technology and the corresponding toolpath generation algorithm are proposed to achieve the flexible fabrication of micro-freeform lens arrays with high AR. In OTS, with the assistance of four-axis servo motions, a spiral toolpath is generated for each single lenslet, which effectively avoids the tool interference induced by the steep descending movement of the tool in F/STS. Besides, the proposed machining strategy well ensures the smoothness of the generated toolpath for each lenslet, thereby effectively avoiding the destruction of the surface quality induced by the tool vibrations. In practice, this method is validated by fabricating different MOAs with aspheric and freeform structures. Compared with F/STS, the OTS method is demonstrated to be able to achieve two times larger AR values, and smoother and more uniform surface quality are simultaneously achieved.