Development of a low cost high precision fabrication process for glass hybrid asphericaldiffractive lenses

Abstract

The hybrid aspherical diffractive singlet achromat design can be used to reduce chromaticaberration in compact optical systems. In this paper, the development of a compressionmolded, low cost and high precision hybrid diffractive glass lens is described. Specifically,an aspherical diffractive lens designed to compensate for chromatic aberration wasfabricated by precision glass molding. The diffractive features are integrated on theaspherical surface to avoid mold alignment during fabrication. As part of the effort to lowermanufacturing cost, the diffractive profiles were directly fabricated by single-pointdiamond turning without polishing. A thin layer of platinum–iridium coatingwas applied to the mold surfaces to protect the mold inserts from degradationduring the molding process. In order to reduce thermal shrinkage error, the hybridlens was fabricated using a two-step precision molding process on a commercialglass molding machine. The geometry of the molded hybrid aspherical diffractivelens was measured using an optical profilometer and the results demonstrated amatch to the design mold profile with a replication error of 0.16% in the radialdirection and 6.3% in the axial direction. In addition, an optical metrology system toevaluate the diffraction efficiency and chromatic focal shift was constructed andthe measured results showed that the hybrid lenses indeed function as designed.