A group of researchers from the University of California at San Diego and Cymer (San Diego, CA) has developed a way of fabricating aspherical polymer lenses with a tunable liquid-filled mold, enabling inexpensive one-off fabrication of prototypes (as opposed to the conventional approach of diamond-turning a rigid mold, which is best for large-volume production). A polydimethylsiloxane (PDMS) membrane is stretched and mounted midway down a well structure; the upper part of the well forms the lens mold, while the bottom of the well contains fluid that is pumped in or out to vary the curvature of the membrane.
Once the right curvature is reached, the top of the well is filled with liquid PDMS, which is cured and then separated from the membrane to form the lens (the lens and membrane easily separate due to lack of chemical cross-links). The lens shape closely matches that of a sphere plus a conic function; as the membrane is tuned, both the radius and conic constant change (the mold dimensions and membrane pre-stretch should be optimized for the desired lens parameters). Fabricated lenses had a surface roughness of less than 6 nm and an aspherical profile with a root-mean-square error of less than 30 nm from the desired conic function. Contact Sung Hwan Cho at [email protected].