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Manufacturing High Numerical Aperture Microlens Array by Microfluidics and Oil-Induced Expandable PDMS Membrane

This paper presents a novel approach to the manufacture of microlens arrays (MLAs). Briefly, a polydimethylsiloxane (PDMS) membrane bonded to a micro-milled poly(methyl methacrylate) (PMMA) microfluidic chip is exposed to silicone oil of various viscosities. Polymer molecules in the silicone oil insert themselves into the molecular structure of the PDMS membrane, causing it to swell into dome-shaped micro lenses. Experiments showed that: (1) uniform swelling of the PDMS membrane successfully resulted in MLAs with a high numerical aperture (0.5); (2) silicone oils with shorter molecular chains (meaning low viscosity) diffused more readily into the PDMS membrane, resulting in MLAs with higher sag height and a higher numerical aperture.