Researchers at the University of Arizona in Tucson and at the University of Oulu in Finland have fabricated a micro-optics imaging system for a miniature microscope using a gray-scale lithographic printing technique with sol-gel glass. They reported the work in the April 5 edition of Optics Express.The scientists employed a "pixelated" gray-scale photomask through which they exposed the photosensitive sol-gel material to ultraviolet radiation. The photomask featured 4 X 4-µm pixels with 129 gray-scale levels ranging in optical density from 0.12 to 1.4. They then immersed the polymerized material in developer to free the 1.3-mm-diameter lenses, which featured a 56-µm sag, and characterized the fabricated elements using an optical profilometer, Fizeau and Mach-Zehnder interferometers, and a Shack-Hartmann wavefront sensor.In a test of the assembled system, which incorporated three of the antireflection-coated lenses, the researchers imaged glass spheres with diameters of 10 to 30 µm and a grating with 600 line pairs per millimeter. They noted that, although the imaging quality of the system is expected to improve, it already can be used to resolve cell-size features.