In-situ-sensing of 3d refractive index distribution during additive manufacturing of GRIN optics (InProGrin)

• Applicants: Professor Dr. Ralf Bernhard Bergmann; Professor Dr. Andreas Heinrich
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539598473

Additive manufacturing has become increasingly important in the production of complex optical components in the last few years, especially in the fabrication of single items or small quantities. An essential prerequisite for the use in large-scale production is the development of precise and highly flexible methods for in-process quality assurance and the evaluation of the optical properties of the components already inside the fabrication process. Especially in the field of additive manufacturing of graded index (GRIN) optics, the state of the art reveals deficits, for the selective manipulation of the refractive index distribution, as well as the in-process monitoring of the manufacturing process regarding to the optical properties of the manufactured optical components. A barrier for the development of in-process quality assurance lies in the fact that there is no comprehensive description in the literature of the influences of the manufacturing process, especially deviations of the designed process, on the optical properties of the fabricated components. However, a comprehensive understanding of these influences is essential for the design of a suitable metrology and the compensation of deviations within the manufacturing process. The project pursues two main objectives. On one hand, the understanding of the influences of the manufacturing process to the polymers and the optical properties of the manufactured optical elements should be improved. This knowledge provides the foundation for a mathematical-physical modelling of the optical properties, considering the properties of the fabrication process. This model will provide the foundation for the development of an algorithm for the compensation of manufacturing deviations and an optimization of the manufacturing process. The second objective is the integration of a fast and robust in-process metrology for quality assurance based on layer-by-layer wavefront sensing. This approach offers the potential to detect and compensate for deviations inside the manufacturing process and consequently to optimize the optical properties of the fabricated optical elements. The result is the starting point for an actively controlled additive manufacturing process. In this context, the selective and reproducible control of the refractive index distribution is a particular challenge from the manufacturing standpoint. The project enables a fundamental extension of the correlation between the optical properties of the manufactured components and the manufacturing boundary conditions. To demonstrate the functionality of the active additive manufacturing process, a GRIN lens will be fabricated.

• DFG Programme: Research Grants