Multi-focusing Microlens Array with Different Numerical Aperture by Thermal Reflow Method

We demonstrate a fabrication method of multi-focusing micro lens array (MLA) through thermal reflow method, and its optical properties. In our multi-focusing MLA, each lens structure was hexagonally packed, and we introduced a partial developing process and a confinement wall structure made by cross-linked photo resist (PR) material to fix a diameter of reflowed spherical lens structure. Due to the base PR layer supporting the thermal reflow process and the guiding structure, the thermally reflowed PR lens structure has different radius of curvatures with different numerical apertures (NAs), where the reflowed PR lens structure could be precisely modeled by the initial volume of the double cylinder PR structure. The multi-focusing MLA we fabricated by using ultraviolet (UV) curable polymer with 1.51 refractive index had four different focal lengths of which values were 0.9 mm, 1.1 mm, 1.6 mm and 2.5 mm, respectively, with four different NAs of which values were 0.1799, 0.2783, 0.3973 and 0.4775, respectively, where the fill factor was 0.7727.