Improved Light Uniformity From Light-Emitting Diodes by Heterogeneous Microlenses and 3-D Printed Mold

We present a novel design and fabrication process using the hydrophilic confinement effect and a 3-D printer for producing convex and concave microlenses on top of light-emitting diodes. We use energy conservation and a lawnmower algorithm to design a freeform lens, and transform it into heterogeneous microlenses. The diameters of the microlenses on top of the light-emitting diode are 500 and 200 μm for the concave and convex shapes, respectively. Heterogeneous microlenses are printed on a glass substrate using the hydrophilic confinement effect of SU-8 photoresist and an inkjet printer. Then, the array is copied with a mold made by a 3-D printer for the replication process. In the replication process, the mold is filled with polydimethylsiloxane to reproduce heterogeneous microlenses. Experimental results show that this heterogeneous microlens array improves the light distribution uniformity of a light-emitting diode from 17% to 63%.