Microlens Arrays Fabricated through Molding

A photopolymerizable water-based liquid was first flowed into the micro-channel and pneumatically squeezed from the apertures by operating a syringe pump to form curved liquid menisci at the liquid-air interfaces at the top edges of the apertures. The radii of curvature of these liquid menisci were determined by three factors (1) the difference between the applied pneumatic pressure and the atmospheric pressure, (2) the surface tension, and (3) the gravity of the liquid. A specific radius of curvature and thus the focal length of the resultant microlenses could be achieved by tuning the applied pneumatic pressure P in the microchannel. 

The sidewalls and bottom surfaces of the apertures were chemically treated to be hydrophilic. The top surfaces of the apertures were naturally hydrophobic based on material surface properties, thereby pinning the liquid-air interfaces along the hydrophobic-hydrophilic boundaries at the top edges of the apertures. 

---

Microlens arrays fabricated through molding processes Injection-molded plastic lenses... 

X. Zeng and H. Jiang, "Polydimethylsiloxane microlens arrays fabricated through liquid-phase photopolymerization and molding," Journal of Microelectromechanical Systems, vol. 17, pp. 1210-1217, Oct 2008. 

These liquid menisci were maintained in a certain convex shape through pneumatic control and throughout the subsequent photopolymerization of the polymer under UV irradiance, after which the polymer transfer molds were formed. Due to its excellent light transparency and mechanical flexibility, PDMS was used as the microlens material. To produce convex PDMS microlens arrays, two molding steps were needed to transfer the fabricated polymerized molding structures to PDMS. Figure 4.32 shows the process flow [26]. 

---