A simple method for fabrication of thick sol-gel microlens as a single-mode fiber coupler

We demonstrate a cost-effective and high-volume fabrication method for building microlenses in hybrid sol-gel material. The fabrication process includes three main steps. First, the microlenses were built in photoresist by a reflowing technique. Second, surface profiles of the microlenses were transferred to an elastic polydimethylsiloxane (PDMS) replica. Finally, the microlenses were fabricated by impressing the replica onto a thick sol-gel film with simultaneous ultraviolet curing. As an example, a microlens with a diameter of 80 μm and a sag height of 13 μm was fabricated for a coupling experiment between two single-mode fibers. A measured coupling efficiency of 2.2 dB (60%) was obtained, which could be further improved to approach the theoretical efficiency of 0.3 dB (93%) with an ultraprecision alignment stage.