6 February 2008 Free-form machining for micro-imaging systems
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While mechanical ruling and single point diamond turning has been a mainstay of optical fabrication for many years, many types of micro-optical devices and structures are not conducive to simple diamond turning or ruling, such as, for example, microlens arrays, and optical surfaces with non-radial symmetry. More recent developments in machining technology have enabled significant expansion of fabrication capabilities. Modern machine tools can generate complex three-dimensional structures with optical quality surface finish, and fabricate structures across a dynamic range of dimensions not achievable with lithographic techniques. In particular, five-axis free-form micromachining offers a great deal of promise for realization of essentially arbitrary surface structures, including surfaces not realizable through binary or analog lithographic techniques. Furthermore, these machines can generate geometric features with optical finish on scales ranging from centimeters to micrometers with accuracies of 10s of nanometers. In this paper, we discuss techniques and applications of free-form surface machining of micro-optical elements. Aspects of diamond machine tool design to realize desired surface geometries in specific materials are discussed. Examples are presented, including fabrication of aspheric lens arrays in germanium for compact infrared imaging systems. Using special custom kinematic mounting equipment and the additional axes of the machine, the lenses were turned with surface finish better than 2 nm RMS and center to center positioning accuracy of ±0.5 μm.
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Michael L. Barkman, Michael L. Barkman, Brian S. Dutterer, Brian S. Dutterer, Matthew A. Davies, Matthew A. Davies, Thomas J. Suleski, Thomas J. Suleski, "Free-form machining for micro-imaging systems", Proc. SPIE 6883, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics, 68830G (6 February 2008); doi: 10.1117/12.769689; https://doi.org/10.1117/12.769689


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