Fabrication of high numerical aperture micro-lens array based on drop-on-demand generating of water-based molds

•A simple high numerical aperture microlens array fabrication method was provided.•The high numerical aperture microlens was replicated from the water-based mold.•The water-based mold was fabricated based on a drop-on-demand droplet generator.•The numerical aperture of the fabricated microlens was 0.62.

This letter presented a simple fabrication method of micro-lens arrays with high numerical aperture based on a new drop-on-demand generating of water-based mold. The micro-droplet array which acted as the water-based mold was generated on the polypropylene substrate using a drop-on-demand generator, and then a replication process was followed for fabricating the micro-lens arrays with high numerical aperture. A spherical-like micro-lens array with the numerical aperture of 0.62 was fabricated. The surface of the formed micro-lens was demonstrated super smooth (Ra~0.5 nm, Rq~0.7 nm, Rmax~13.2 nm, 2×2 μm2 scanned area) by the atomic force microscope, which can reduce the optical noise. The qualities of imaging and light gathering characteristics of the MLAs were evaluated by the optical microscope.