Fabrication of novel double microlens using two step soft lithography

A novel method to fabricate double layer microlens array is proposed where the second smaller microlens are imprinted on the first larger microlens by using soft lithography twice. Key step to implement this method is to imprint micron-size structures on convex surface using nano-imprinting technology. It is required to prepare thin polydimethylsiloxane (PDMS) mold for the second soft lithography and thus different thickness of PDMS molds have been tested. It is found that 870 μm thick mold is good for fine duplication and durability. We have successfully fabricated the first microlens hemisphere of 51 μm diameter and the second microlens of 3 μm diameter on top of the first. The double microlens array shows more focused light spot when viewed through optical microscope.