A Multiphase Printing Process for Freeform Optics Manufacturing

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Freeform optics can form high quality images with smaller aberrations by using fewer optical components. At the present time, fabrication of a freeform optical component is extremely time consuming. Drop-on-demand printing has been used to fabricate spherical or aspherical microlenses with simple curvatures, but is not able to produce more complicated designs due to the constraint of symmetric surface tension forces. By applying external interfacial forces, this constraint can be overcome and freeform shapes can be formed. This award supports fundamental research of a novel multiphase printing process that integrates direct printing and interfacial forces in order to fabricate high precision freeform micro optics. This project will benefit the U.S optical industry by providing a new high precision manufacturing process for low-cost and high quality optical products. Research results can be readily applied to other manufacturing areas that utilize tunable interface forces, for example, 3D printing of smooth streamline surfaces in aerospace, automobile, and biomedical industries.The research objectives are to establish relationships (1) between lens surface curvatures and the multiphase conditions (such as thickness and tilting of the supporting liquid phase); (2) between freeform lens profiles and dynamic deformation of droplets; and (3) between the freeform lens shapes and non-uniform material properties (e.g. different surface tension and viscosity coexisted on the droplet surface). Experiments will be conducted on a hybrid multiphase printing platform. On this platform, ultraviolet curable monomer droplets will be printed on a solid-liquid-air or liquid-air multiphase surface under different multiphase conditions. A precision linear and tilting stage will be used to control the thickness and tilting of the supporting liquid phase. Lens surface curvatures will be measured by a white light interferometer and a combined Twyman-Green and Mach-Zehnder interferometer. To achieve the first objective, monomer droplets will be cured after the droplets reaching equilibrium status on the multiphase surface. Finite element method will be used to determine lens profile curvatures under different multiphase conditions. To achieve the second objective, monomer droplets will be cured at transient state. A high speed camera will be installed to identify the droplet transient shape. Lens profiles obtained at different transient state will be analyzed and correlated to high speed images. To achieve the third objective, maskless lithography will be used to tune the local surface tension and viscosity of the monomer droplet to achieve non-uniform properties, which will cause non-uniform droplet deformation.