Freeform manufacturing of a microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo

Abstract

We report what is to our knowledge the first approach to diamond turn microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo. In recent years ultraprecision machining has been employed to manufacture accurate optical components with 3D structure for beam shaping, imaging and nonimaging applications. As a result, geometries that are difficult or impossible to manufacture using lithographic techniques might be fabricated using small diamond tools with well defined cutting edges. These 3D structures show no rotational symmetry, but rather high frequency asymmetric features thus can be treated as freeform geometries. To transfer the 3D surface data with the high frequency freeform features into a numerical control code for machining, the commonly piecewise differentiable surfaces are represented as a cloud of individual points. Based on this numeric data, the tool radius correction is calculated to account for the cutting-edge geometry. Discontinuities of the cutting tool locations due to abrupt slope changes on the substrate surface are bridged using cubic spline interpolation.When superimposed with the trajectory of the rotationally symmetric substrate the complete microoptical geometry in 3D space is established. Details of the fabrication process and performance evaluation are described.

Replication of optical microlens array using photoresist coated molds

“…Direct fabrication of lens arrays by diamond turning in polymer materials have been demonstrated [23][24][25][26][27][28] to achieve the high optical surface quality. Although the direct diamond turning process is a one step process, due to process difficulty and expensive tooling, the fabrication process cost could be in the order of USD 100 -1000 /mm 2 .…”

Corrective polishing of freeform optical surfaces in an off-axis three-mirror imaging system

“…In spite of its advantages, freeform optics also brings challenges for manufacturing and measurement. Diamond turning [2,3], freeform milling [4], and ultra-precision grinding [5,6] are usually used for machining the freeform optics, but the machined surface cannot meet the requirements of optical applications because of the surface textures left by premachining processes, a further finishing process is inevitably required after the pre-machining process.…”

Theoretical and experimental investigation on the novel end-fly-cutting-servo diamond machining of hierarchical micro-nanostructures

“…In diamond cutting, by means of fast tool servo (FTS) or slow tool servo (STS), true three-dimensional (3D) artificial compound eyes (ACEs) can be well generated [11][12][13]. With the 3D ACEs, the primary surface was spherical with a small curvature, and imposition of secondary micro-prism arrays as well as micro-sphere arrays on the primary curved surface were generated by freeform machining.…”