Dynamically adjustable three-dimensional gray masks operated by electrostatic force modulation for the fabrication of microlens arrays in microchannels

Abstract

We propose a new approach to fabricating micro-optical elements, in particular, microlenses and microlens arrays using an adjustable gray-scale mask and a microfluidic conveyor module. A liquid with acrylate oligomer is photopolymerized while it flows through this module, thus forming the micro-optical components. The adjustable gray-scale mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses. By applying a high voltage, the shape of these microlenses can be altered, enabling one to change the intensity transmission distribution of the gray-scale mask and, as a consequence, the surface profile of the corresponding microlens structures in the microfluidic conveyor module below. The produced microlens structures are washed out of the conveyor module without adhesion on the walls of the PDMS microchannel surfaces due to the existence of an oxygen-aided inhibition layer. The dependence of the produced microlens morphology on the index-matching oil, the concentration of UV-absorbing liquids, and the electrostatic force modulation of the adjustable gray-scale mask are characterized. The adjustable gray-scale mask combined with a suitable flow/stop sequence enables one to fabricate microlenses and microlens arrays in a continuous and high-throughput mode.