Polydimethylsiloxane Microlens Arrays Fabricated Through Liquid-Phase Photopolymerization and Molding

We report on polydimethylsiloxane (PDMS) microlens arrays fabricated through liquid-phase photopolymerization and molding. The gist of this fabrication process is to form liquid menisci of variable radii of curvature at an array of apertures through pneumatic control, followed by photopolymerization under ultraviolet radiance. The resultant polymerized structures are then transferred to PDMS utilizing two molding steps. By adjusting the pneumatic pressure during the process, a single aperture array can be used to fabricate PDMS microlens arrays with variant focal lengths. The liquid menisci are formed by liquid-air interfaces that are pinned at the top edges of the apertures along hydrophobic-hydrophilic boundaries generated through surface chemical treatments. The microlens arrays are optically characterized. Variant focal lengths from 2.35 to 5.54 mm and f-numbers from 1.27 to 5.88, dependent on the diameter of apertures and the applied pressure to form the liquid menisci, are achieved with this relatively simple process and match well with the physical model. Owing to the formation from the liquid-air interfaces, the surface roughness of microlenses is measured to be around 25 nm.

I. Introduction

Microlenses are important optical components and have been extensively studied for many years [1]–[6]. Among these microlenses, microlens arrays have found many applications, such as photolithography [7], [8], optical communications [9], [10], microimaging systems [2], [11], [12] and lab on chips [13]–[15]. Benefiting from the small surface roughness at immiscible interfaces involving liquids, the microlens surfaces formed in most fabrication processes are based on the liquid–liquid or liquid–air interfaces, including plastic hot intrusion [16], photoresist thermal reflow [2], [7], [14], [17]–[19], inkjet printing [20], and isotropic etching [14], [21]. However, these fabrication methods generally have limited flexibility in patterning microlenses with different focal lengths.