Experimental investigations on the development of hybrid optical surfaces by using ultra-precision machining

Hybrid optical surfaces are gaining attention for system miniaturization and enhanced optical throughput, but challenges arise in creating precise tool paths for dual profiles with consistent micro-grooves and minimal form errors. In this study, an innovative retract toolpath approach is reported to fabricate hybrid surfaces with high-quality finish using the 2-axis configuration of a diamond turning machine. A hybrid surface with a 5 mu m feature size on a 38 mm radius spherical profile was fabricated using a 6.35 mu m nose radius diamond tool, with 1000 rpm spindle speed, 0.1 mm/min feed rate and 2 mu m depth of cut. The retract toolpath approach offers better control over feature size, pitch and groove depth in microstructures than the continuous method. The proposed approach, validated on aluminum, brass and PMMA, demonstrated form errors below 0.63 mu m and surface roughness under 4.5 nm. The results show that the proposed tool path approach is suitable for maintaining precise microstructuring over curved surfaces and for different materials to cater to the needs of wide application fields. Specifically, for compact systems in widespread visible and near infrared applications, which require precise and miniaturized optical components to enhance the field of view and resolution of the systems.