Chromatically multi-focal optics based on micro-lens array design

CCD arrays encode color information via uniformly distributed red, green and blue pixels. Therefore, even a perfectly achromatic system projecting an image onto a CCD plane cannot possibly associate a single object point with the 3 or more discrete pixels encoding color content. Here, we propose and demonstrate a micro-lens array (MLA) design that simultaneously corrects chromatic aberrations and separates color channels to spatially distinct pixels. Starting from a commercially available aspheric condenser lens, methods to design and assess the performance of a few microns deep MLA etched on the convex optical surface are detailed. Actual fabrication is carried out by fluid jet polishing, with an optical form deviation of 0.24 µm rms. Finally, the MLA is assessed with a narrowly collimated beam containing two wavelengths, which produces distinct spots of diameter 10-15 µm as expected.