Ultralong focal length microlens array fabricated based on SU-8 photoresist

In this paper, a novel method to fabricate ultralong focal length microlens arrays has been proposed. The microlens arrays were fabricated based on surface tension when heating temperature is over a glass transition temperature of SU-8 photoresist. An ultralong focal length was achieved by the large radius of curvature of a photoresist surface. Microlenses of widths from 30 to 210 μm were successfully fabricated. The longest focal length was up to 4.4 mm from the microlens of 210 μm width. The formation mechanism was also studied and validated by simulation based on the finite element method.