Soft-lithography-enabled fabrication of large numerical aperture refractive microlens array in hybrid SiO2–TiO2 sol-gel glass

This paper describes a low-cost soft-lithography method for building large-numerical-aperture microlenses in hybrid sol-gel glass. The fabrication processes comprise three steps, namely fabrication of large numerical aperture microlens array in photoresist as a master, replication of the master in poly-dimethylsiloxane (PDMS) as elastomeric molds and reproduction of the PDMS replica onto the hybrid sol-gel glass as an end structure. Comparing with the direct UV fabrication in the photosensitive sol-gel glass, the proposed method provides a unique advantage in terms of fabrication freedom in shape and thickness of micro-optical elements in the sol-gel glass. This eliminates the difficulties in direct photolithography in sol-gel glass for arbitrary shapes and great thickness due to ever increasing demands.