Influence of tool geometry on single-crystal CaF₂ in an ultra-precision machining

Optical signal processing circuits can realize ultimately efficient signal processing. Optical micro-cavities, which can localize light at certain spots, are important components for the circuits. Single-crystal calcium fluoride (CaF₂) is the most suitable material for highly efficient optical micro-cavities, and ultra-precision cylindrical turning (UPCT) is a feasible fabrication process for CaF₂ optical micro-cavities. However, CaF₂ is characterized by brittleness and crystal anisotropy; therefore, it is necessary to prevent microcracks in UPCT because such cracks would lead to light scattering and cavity performance deterioration. In this study, we conduct plunge-cut tests on CaF₂ substrate with various single point diamond tools, and experimentally investigate the influence of tool geometry and process parameters on critical depth of cut. Based on the experimental results, enhancement of CaF₂ micro-cavity is attempted.