Fabrication of Hexagonal Microlens Arrays on Single-Crystal Silicon Using the Tool-Servo Driven Segment Turning Method

Single-crystal silicon microlens arrays are increasingly required in advanced infrared optics. In this study, the authors attempted to fabricate hexagonal microlens arrays, which offer high optical efficiency, on a single-crystal silicon wafer using diamond turning. A tool-servo driven segment turning method was proposed to reduce the dynamic error of the machine tool induced by lenslet edges during lens array cutting. From the results of both cutting experiments and theoretical analysis of the machine tool dynamic error, it was demonstrated that the segment turning method reduced significantly the dynamic errors and led to high form accuracy. As a result, sharp edges among the lenslets were generated precisely and microlens arrays with a form error of similar to 300 nm peak-to-valley and surface roughness of similar to 5 nmSa, which meets the requirements of infrared optical systems, were successfully fabricated. The subsurface damage, such as the amorphization of silicon, caused by machining was also reduced.