A Rapid Fabrication Method of Large-Area MLAs with Variable Curvature for Retroreflectors Based on Thermal Reflow

Abstract

Retroreflectors are an important optical component, but current retroreflector structures and manufacturing processes are relatively complex. This paper proposes a rapid, low-cost, large-area method for fabricating retroreflectors based on microlens arrays. Tunable microlens arrays with adjustable curvature, fill factor, and sizes were prepared using photolithography and thermal reflow techniques. Subsequently, a two-step nanoimprinting process was used to create a flexible reverse mold and transfer the structure onto the desired substrate. The microlens arrays, with a diameter of 30 μm, a period of 33 μm, a curvature radius ranging from 15.5 to 18.8 μm, and a fill factor ranging from 75.1% to 88.8%, were fabricated this way. In addition, the method also fabricated microlens arrays with diameters ranging from 10 to 80 μm. Retroreflectors were made by sputtering a layer of silver on the MLAs as a reflecting layer, and tests showed that the microlens-based retroreflector exhibited superior retroreflective performance with a wide-angle response of ±75°. Microlens-based retroreflectors have the advantages of simple operation and controllable profiles. The fabrication method in this paper is suitable for large-scale production, providing a new approach to retroreflector design.