Various fabrication techniques have been developed in the last decades to allow for the manufacturing of high-quality optics at small cost in large volumes. From an optical performance point-of-view, significant improvements can be obtained when a freeform optical profile is used over a traditional spherical lens shape. Indeed, this allows for minimizing the number of optical surfaces (and thus the size and weight of the component) needed for minimal optical aberrations and maximal optical performance. However, freeform lens shapes are much more difficult to fabricate than their traditional, spherically-shaped and rotationally-symmetric counterparts.
An interesting approach providing full 3D design freedom is the use of two-photon polymerization-based laser direct writing. While this technique allows 3D printing of arbitrary shapes with sub-micrometer resolution, it is mostly limited to component sizes of up to a few hundreds of micrometers. For larger optics, one has to divide the structure to be printed in several parts, which significantly increases the printing time, and the transition between these parts is typically not seamless.
The authors of this recent Optical Materials Express paper show that this technique can also be used for larger lenses in the millimeter size range without introducing stitching artifacts. In addition, they also propose the use of a novel polymer material that doesn’t turn into a yellowish color after polymerization, compared to those commonly used for laser direct writing, and therefore strongly improves the transparency of the optical components made with this new material, positively impacting the resulting optical performance.
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