Ductile machining of optical micro-structures on single crystal germanium by elliptical vibration assisted sculpturing

Microstructure surfaces are widely and deeply applied in optical fields to decrease the volume of an optical system and realize sophisticated optical requirements. This paper studies the machining of optical micro-structures with micro-scale height on single crystal germanium by elliptical vibration assisted sculpturing (EVAS) method in which two vibration amplitudes keep constant. Due to the superimposition of low-frequency sculpture path and high-frequency elliptical locus, the investigations are focused on cutting plane to describe motion trajectory of the tool tip of cutting tool for desired complex motion path and to calculate the sculpture path of elliptical vibration cutting device to make corresponding path of tool tip be the envelope of target profile. A comparative experiment is firstly conducted to verify that elliptical locus would deteriorate machining accuracy without accurate compensation for the ellipse. Following that, 2D and 3D sinusoidal surfaces and a picture, whose structural heights are all not less than 2.0µm, are experimentally machined on single crystal germanium. Satisfying experimental results demonstrate the feasibility of EVAS method for fabricating optical micro-structures on germanium.