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Microforging technique for rapid low-cost fabrication of lens array molds

Interest in micro-optical components for applications ranging from telecommunications to life sciences has driven the need for accessible, low-cost fabrication techniques. Most micro-lens fabrication processes are unsuitable for applications requiring 100% fill factor, diameters around 1 mm, and scalability to large areas with millions of lenses. We report on a ﬂexible, low-cost mold fabrication technique that utilizes a combination of milling and microforging. The technique involves first performing a rough cut with a ball-end mill. Final shape and sag height are then achieved by pressing a sphere of equal diameter into the milled divot. Using this process, we have fabricated molds for rectangular arrays of 1-10,000 lenses with apertures of 0.25-1.6 mm, sag heights of 3-130 &mgr;m, inter-lens spacings of 0.25-2 mm, and fill factors of 0-100%. Mold profiles have roughness and ﬁgure error of 68 nm and 354 nm, respectively, for 100% fill factor, 1 mm aperture lenses. The required forging force was modeled as a modiﬁed open-die forging process and experimentally verified to increase nearly linearly with surface area. The process is easily adapted to lenticular arrays. Limitations include milling machine range and accuracy.