Reik Krappig, Fraunhofer IPT: High-tech meets craftsmanship
The Fraunhofer Institute for Production Technology bundles its competencies in the production and evaluation of complex optical components in its Optics business unit. A wide range of production stages are covered along the entire value-creation chain. Reik Krappig is head of the Optics business unit at Fraunhofer IPT.
1. Grinding and polishing are core technologies in the production of glass optics. What is the current state of technology here?
Reik Krappig: Grinding and polishing continue to be important production technologies for the optical industry. And today a significant proportion of all optical components is still being produced in very high precision using these technologies. As a result, we also see continuous further development in this area. Thanks to sub-aperture and fluid jet polishing, for example, complex and even nonrotational symmetrical geometries can be polished. With a view to current research topics in optics, however, grinding and polishing no longer play a central role. The pace of this process's development tends to be not as fast as it is with replicative or generative processes.
2. The constant demand for increasing imaging quality along with decreasing costs can barely be met any more with grinding and polishing. What new approaches could replace conventional production here?
Reik Krappig: Replication processes, with which the comparably high cost of producing the molding tool is spread over the amount of components produced, are suitable for production processes in high unit volumes. One possibility here is the precision molding of optical glass components.
The technological capability and cost effectiveness of such replication processes, however, depend heavily on the specific application. Compare, for example, the production of a quartz glass lens with the production of an infrared-transmissive chalcogenide lens: regardless of the geometry, quartz glass components require absolute material-conditioned forming temperatures of approximately 1400° Celsius. The chalcogenides, however, can already be formed at less than 250° Celsius. High temperatures entail strong demands on the accompanying molding tool.
3. Lower to more mid-range quality requirements with mid-range and high unit numbers – one thinks immediately of plastics. To what degree and in what areas have polymers already replaced glass in optics production?
Reik Krappig: At first glance they both have their very own special features, which make them ideal for various areas of application. With a microscopy lens, glass will surely be used, but the optical head of a room light is probably produced with a polymer.
This consideration becomes interesting in the areas at the limit: despite their high efficiency level, increasingly higher luminosity LEDs not only emit luminous flux of more than 1,000 lumens. They also get especially hot and therefore require an optical attachment that can constantly withstand theses temperatures. As a result, glass is experiencing a comeback today in areas it had apparently lost. On the flip side, polymers are also blazing their own trail in conventional areas of glass optics. Examples include optical silicones, which remain temperature stable up to almost 200° Celsius, and injection-molded micro-lenses, which are aspherical on both sides, have aperture diameters of around one millimeter and are used for endoscopic imaging systems.
And even if the trend appears to be developing in favor of plastics on the whole, it is still exciting to watch how both material classes develop.
4. Optics and precision are seemingly two terms that are inseparably connected with one another. How do you ensure exactness with what have now become very extreme tolerance limits?
Reik Krappig: Production technology and metrology constantly compete, not just to produce demanding geometries, but also to be able to analyze using measurement technology. Functional integration and miniaturization result in increasingly lower tolerance limits. Production technologies are now quite often one step ahead of measurement technology.
Because, among other things, the accuracy of the measurement equipment has to ideally be a factor of 10 higher than the variable to be measured, requirements emerge that frequently cannot be met with the available devices.
This is also the reason why the measurement technology still has to be continuously refined. It has to maintain its ability (or recover it again) to precisely characterize components produced with high precision as well as suitably monitor production.
5. You recently called for a consortium study entitled "The limits of optics production." Where do you see these limits?
Reik Krappig: The optics industry is an extremely technology-driven, highly innovative sector. Many small companies operate in valuable niches with specific technologies. These can be special sensors or the production of specific components. The accompanying technologies frequently operate in areas at the limit of the technically feasible and must be further developed under these special conditions.
The limits do not, therefore, only apply to specific materials here. And with regard to optics design and the production process, there are always new possibilities that must be sounded out. Ultimately then, this also applies to measurement technology. As a result, we see four major guiding topics that will develop rather dynamically in coming years. With the study, “The limits of optics production,” we want to illustrate such developments in cooperation with research and industry.
6. Whats benefits are there for participating companies?
Reik Krappig: By participating in the study, companies can jointly determine the specific arrangement of the content within the scope of the four guiding topics. This in turn creates an immediate benefit for the respective company, which receives scientifically valid information on state-of-the-art technologies that are important to the company's own production or could become so.
The study's consortium also offers a suitable platform that participating companies can use to learn about what is going on beyond their own activities. As research partners, we work together to prepare essential information that can be extremely important for mid-term technology planning. Supplemented by market figures that we have extrapolated to the coming five to ten years, the study also holds high strategic value.