Imagine a window pane was several centimeters thick. “Everything would have a distinct color gradation, and you would have trouble seeing through it,” explains fiber optics expert Lothar Willmes, Head of Product and Technology Development Fiber Optics at SCHOTT Lighting and Imaging. “The reason for this is that the soda-lime glass used to make most windows isn’t very high quality, and so the light quickly degrades while traveling through it.” In contrast, high-quality glass optical fibers can transmit white light over 10 to 15 meters with almost no loss and little degradation in quality. High-quality light transmission is critical for many applications, including the light guides inendoscopes used for tissue analysis. For a precise diagnosis, it is extremely important that tissue color be reproduced with as little distortion as possible.
This is where PURAVIS® glass fibers come into play. These widely-known fibers have a typical structure consisting of a glass cladding only micrometers thick surrounding a solid optical core with a distinctly altered refractive index. Where these two glasses meet, the light is entirely internally reflected and thus transmitted down the fiber with barely any loss. The high-tech, in house glass used in SCHOTT’s fibers allows the cladding and core to be finely calibrated to each other. The characteristics of the two glasses can be precisely optimized to create specific optical properties, such as certain light entry and exit angles.
Most of these fibers start as a rod several centimeters thick and one meter long. They are installed on the second floor of the multiple fiber line draw tower used to carry out SCHOTT’s completely unique multiple fiber drawing process. The process begins by simultaneously heating many rods in a patented, precisely controlled furnace. Once hot, the glass is drawn downwards by gravity until a bundle of exceptionally fine glass fibers is formed. The fall distance over two floors allows fibers with diameters of just 30, 50 or 70 micrometers to cool and set before being wound up.
Willmes stands on the ground floor next to the precision winder that rolls the filigree fiber bundleonto spools. He has been involved and significantly shaped the company’s glass fiber production over the last 35 years. This precise winding technology, developed and patented in-house, allows several hundred meters of glass fibers to be wound onto a spool at high speeds without any breakage. On these spools, fibers can be handled efficiently – a prerequisite for their cost-efficient further processing. It also allows SCHOTT to supply customers with single fibers, fiber bundles or extruded bundles enclosed in an elastic plastic sheath according to individual specifications.
The tightly regulated medical technology industry and environmental protection requirements both place high demands on glass. For one, it must be free of toxic lead. “Normally, additives such as lead are used to raise the quality of glass and glass fiber production – the main reasons being that they can be used to adjust optical properties and also remove any flaws such as air bubbles during the so-called refining process,” says Willmes. “Thanks to extensive research and development work, we have created a process that doesn’t use these types of undesirable materials.” SCHOTT has developed and patented its refining technology with more than 30 patents that protect the production of PURAVIS® fibers.
After more than 35 years, Willmes says he still isn’t bored studying glass fibers. “Customers keep coming back with new, special requests and suggestions,” he says. “For example, these fibers are now being used in the first single-use endoscopes, which are just now entering the market.” Close internal networking enables SCHOTT to offer customers services ranging from customized solutions to industrial mass production.