MEMS and optical systems—increasingly in miniaturized form—are essential components of our daily lives. In addition to lens-based axial optical systems, such as those used in most camera optics—particularly in cell phones—non-axial mirror-based optical systems offer great potential for spectrally demanding applications. The advantage of eliminating lens chromatic aberration and absorption in the lenses is offset by the challenge of complex assembly and alignment of the optical components. This has so far prevented widespread market adoption, for example, of compact near-infrared spectrometers in food applications or multispectral cameras for driver assistance.
A novel approach by Fraunhofer IPMS—the folding assembly of planar substrates, inspired by the Japanese art of paper folding known as “origami”—could eliminate these limitations and significantly improve the current state of the art. In this technical approach, a planar substrate is provided with bending structures along precisely adjustable bending lines. After the components are mounted using available high-precision 2D placement machines, the three-dimensional structure is created by folding the planar substrate, automatically forming the complex optical path inside. If sufficient accuracy is achieved for the substrate, the component placement, and the folding process, no time-consuming subsequent adjustment steps are necessary. In preliminary research projects, camera systems and NIR spectrometers have already been successfully realized using substrates produced via additive manufacturing (3D printing). The fundamental suitability of injection molding processes for folded assembly was demonstrated in collaboration with the Institute for Polymer Materials and Plastics Technology (PuK) at Clausthal University of Technology. To transition this technical approach to volume production, validation of the “Process chain for fold assembly of miniaturized complex optical systems” (ProFamOS) is necessary.
Building on previous research projects, this project aims to achieve key innovations: (1) demonstrating high-precision injection molding for the production of substrates suitable for mass production and scalable in size, (2) identifying preferred materials—including, where appropriate, filled polymers or even multicomponent substrates— (3) the current manufacturing accuracy will be increased by an order of magnitude, and (4) optical functional surfaces will be integrated, and design rules will be established to efficiently translate the optical design into a substrate design using CAD.
Building on these innovations, additional key project objectives include the development of a complete (micro) injection molding and tooling concept for future production, as well as the realization of two functional demonstrators for systems based on the foldable assembly approach: A multispectral camera for the passenger car mirror base shows potential for use in driver assistance systems, and a NIR spectrometer shows equal potential for mobile spectral analysis in applications within the agricultural and food sectors.