3D fabrication of spherical microlens arrays on concave and convex silica surfaces
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Three-dimensional (3D) microlens arrays are a group of micro-optics structures on curved surfaces that offer unique optical functions such as wide field of view in a compact arrangement. This paper reports an improved rapid lapping and molding system for 3D fabrication of spherical microlens arrays on non-planar surfaces including concave and convex surfaces for optical applications. Unlike traditional approaches for 3D micro patterns on curved silicon/silica substrates, this research demonstrates a low-cost and efficient chemical mechanical polishing process by lapping precision microlenses with steel balls and diamond slurries. Different from lapping on plane surfaces, lapping parameters for each micro cavity need to be accurately calculated and controlled to obtain microlenses with same apertures. Therefore, a micro wear model for micro cavity lapping process was established to calculate cavity sag height with the knowledge of down force, relative velocity and lapping time. Several groups of microlenses lapping were then conducted under the same conditions to validate the micro wear model. Guided by the micro wear model, two groups of microlens arrays were fabricated on concave and convex surfaces respectively. The shape accuracy and surface texture of the microlens arrays were evaluated by using a white light interferometer. Afterwards, the silica molds were coated with graphene film and then utilized to copy the 3D microstructures onto polymers by rapid surface molding. The wide angle imaging characterization of the 3D polymeric microlens arrays was illustrated by a simple optical setup and the measured MTF curves using the slanted-edge method. The improved manufacturing platform demonstrates a new approach for 3D microlens arrays fabrication on hard substrates in a cost effective way.
This study was partially based on the work supported by National Science Foundation under Grant Number 1537212. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors would also like to acknowledge support of an NSF SBIR Phase I and Phase II program from Nanomaterial Innovation LLC under the Grant Number 1315009 and 1456291. The work was also supported by National Natural Science Foundation of China (No. 51775046). Xiaohua Liu acknowledges the financial support from China Scholarship Council.
- Liu X, Zhou T, Zhang L, Zhou W, Yu J, Lee LJ, Yi AY (2018b) Fabrication of spherical microlens array by combining lapping on silicon wafer and rapid surface molding. J Micromech Microeng 28(7):075008Google Scholar