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Microlens array fabrication through crosslinking photopolymerization

Growing interest in miniaturized optical components for various applications such as optical interconnection systems and telecommunication industry have led to the development of several techniques that are used in the fabrication of micro-optical elements. One approach involves the use of polymers as recording materials: these are flexible, highly transparent and cheap. The technique described in the present paper is founded on the ability of self-processing photopolymers to generate refractive microlens arrays. Spatially controlled illumination of a photosensitive layer induces an inhomogeneous photopolymerization involving a mass-transport process of reactive species and generating a relief in the photopolymer layer. The presentation focuses on the fabrication of microlens arrays through photopolymerization with the green line of an argon-ion laser. Surface tension and differential volume shrinkage turned the illuminated area into good quality lenses. The fabricated lens arrays exhibit diameters ranging from less than 20 micrometers to more than 500 micrometers and focal lengths from 100 micrometers to a few millimeters, depending on photonic, optical and physico-chemical parameters. This imaging technique is highly flexible as regards height, shape and optical properties of the lenses that are produced. By starting from the same background, one can also fabricate diffractive optical elements such as gratings and duplicate computer-generated holograms that come increasingly into prominence as the micro-opto-electro-mechanical field expands.