In many devices and systems, such as telescopes, light barriers, cameras, laser measurement technology, and smartphones, optical filters ensure that light is reflected or transmitted depending on its wavelength.
Researchers at Karlsruhe Institute of Technology (KIT) have developed new materials and innovative process technology to produce such filters with an inkjet printer. They demonstrated at Hannover Messe 2023 how custom optical filters and dielectric mirrors could be manufactured inexpensively and energy-efficiently.
“Optical mirrors and filters are needed wherever light is involved in your work,” explains Professor Uli Lemmer, Head of the Light Technology Institute (LTI) at KIT. “Until now, however, they have been manufactured in complex vacuum systems that consume a lot of energy and material and have a comparatively low throughput.”
Optical filters consist of many nanometer-thin, superimposed layers that are built up on top of each other. Mostly, these layers consist of two different materials with different layer thicknesses and refractive index. In conventional production methods, the material is evaporated over a large area so that many material losses occur. These evaporation techniques need very high temperatures and are, therefore, very energy-intensive.
With their novel process, the research team intends to reduce manufacturing costs and flexibly adapt the product’s properties to the respective application. That’s why the researchers used inkjet printers to create inkjet optical filters (IJPOFs).
To do this, they used two different inks specifically designed for this task. The first ink is printed drop by drop until the layer reaches the desired thickness. Then the product is cured with UV light. The next layer is made from the second ink using the same method. Inkjet printers thus produce optical filters layer by layer using two materials that are applied alternately.
Researchers say the applications that have a high demand for the filters produced by inkjet printers include spectroscopic procedures in medicine, metrological devices for the chemical industry, or telescopes with a high reflectance that need to cover a large surface.
The team used the novel inkjet printing process to produce not only optical filters but also dielectric mirrors. The filters have an ultra-high reflectance value of 99% and custom optical properties. The manufacturing method is suitable for optical components in the micrometer range, which are used in cameras, but also for large surfaces such as PV modules.
Uli Lemmer and his doctoral researchers aim to lead this innovative technology for the production of a new generation of optical filters and mirrors to commercial success by founding a spin-off company.