Vacuum-assisted precision molding of 3D thin microstructure glass optics

The continuously rising demands in the today's photonic market towards increasing precision, high surface finish, geometrical complexity yet low cost for thin microstructure glass optics require advanced fabrication technologies. The conventional method via grinding and polishing is limited to those applications mainly due to the unavoidable deformation caused by mechanical stress between lenses and clamping parts. Over the last decade, replication technology such as thermal slumping has become an advanced method in manufacturing complex and precision thin lenses. However, the technology efficiency is strongly diminished by incomplete glass flow into mold cavity and extremely long processing time. In contrast, such deficits can be avoided by a novel molding process with vacuum assistance, recently developed at Fraunhofer IPT. The vacuum-assisted molding promises an effective and reliable technology in the fabrication of high precision thin glass optics for mass production. In this paper, the newly developed molding concept is firstly presented. Besides, this research introduces a numerical implementation based on an enhanced material model characterizing glass behavior at high temperature near softening point, which is crucial to study the internal stress, surface tension and form accuracy of the thin glass. With the help of simulation, the influences of process parameters will be discussed. Experiments were performed for the validation, and the accuracy of the molded glass with microstructure features is discussed in detail. Finally, the experiment results of both thermal slumping and vacuum-assisted molding are compared to illustrate the process efficiency and guidance for industrial applications is delivered.