Ultraprecision machining techniques for the fabrication of freeform surfaces in highly integrated optical microsystems

摘要

The application of multi-axis micromilling and flycutting is investigated for the fabrication of complex optical microsystems incorporating different classes of aspherical and freeform optical elements. Such elements provide the necessary degrees of freedom for aberration correction in integrated optical microsystems and are specifically interesting for applications like beam shaping or computational imaging. Especially for elements with small radii of curvature, high aspect ratios and spatial frequencies, micromilling and flycutting are interesting alternatives to the more established diamond turning technology. We present the results of the fabrication of a monolithically integrated optical microsystem consisting of two tilted flat surfaces used as coupling prisms and a freeform imaging element. On the resulting surfaces the average roughness height without subsequent polishing was found to be R_a= 18.2 ... 25.5 nm (depending on the fabrication technique) with an overall shape accuracy <0.5 ... 2.9 μm (based on the determination of the radii of curvature).