Fabrication of bifocal microlens arrays based on controlled electrohydrodynamic reflowing of pre-patterned polymer

An easy method based on electrohydrodynamic (EHD) reflowing of pre-patterned polymer is proposed in this study for the fabrication of bifocal microlens arrays (MLAs). The method comprises two sequential steps, i.e. hot embossing for generating a polymer-based micropillar array and EHD reflowing of the micropillars for the formation of a bifocal MLA with controllable surface shape and optical performance. The EHD reflowing process is achieved by applying a voltage across an electrode pair sandwiching an air gap and the pre-patterned polymer, and the EHD force induced on the air-polymer interface reshapes the pillar array into the MLA. The complex bifocal microlens can be achieved only when the electric intensity is stronger than that required to produce a commonly known Taylor cone, which is formed when the EHD force exactly surpasses the surface tension. Finally, the light through MLA is imaged on a moving charge-coupled device (CCD) camera and leads to an observation of two focal planes.