Millimeter-Sized Lens Array on Polymer Surface

A shallow lens array with hexagonally arranged millimeter-sized features is fabricated on thin, transparent and flexible polymer layer. A rapid, single-step inexpensive technique is demonstrated for the fabrication using soft- imprint lithography method. The patterned polymer layer is planar on one side and has concave dimples on the other side. The individual features have a size of 2 mm and the array shows efficient focusing characteristics with focal length of 4.891 mm and numerical aperture of nearly 0.205. The optical property of the patterned surface is studied with a pixel-level analysis of the recorded spot size, and is presented as the validation of the lensing nature of the surface. The extremely simple method for making the millimeter lens array has yielded a thin surface which possesses the focusing effect with a short focal length and diverges at larger distances. It can serve as an ideal diverging lens for the small-sized light sources such as LED and OLED, as well as a portable lens for viewing small objects in inexpensive microscope designs.