Simulation and Measurement of Refractive Index Variation in Localized Rapid Heating Molding for Polymer Optics

Localized rapid heating process utilizing carbide-bonded graphene-coated silicon molds is a high-efficiency and energy-saving technique for high-volume fabrication of polymer optics. The graphene coating is used as a rapid heating element because of its high thermal conductivity and low electrical resistivity. However, the optical property of molded polymer and its dependence on process conditions such as heat transfer have not been thoroughly investigated. In this research, finite element method (FEM) simulation was utilized to interpret temperature changes of the graphene coating and heat transfer between graphene and polymethylmethacrylate (PMMA) in localized rapid heating. Experiments were then carried out under different voltages to validate the numerical model. In addition, refractive index variation of the PMMA lens resulting from nonuniform thermal history in molding was demonstrated by simulation modeling as well. Finally, wavefront variation of a PMMA lens molded by localized rapid heating was first studied using an FEM model and then verified by optical measurements with a Shack-Hartmann wavefront sensor (SHWFS). The wavefront variation in a PMMA lens molded by conventional method was also measured. Compared with conventional molding process, localized rapid heating is shown to be a possible alternative for better optical performance with a much shorter cycle time.