A group of researchers at the Fraunhofer Institute, headed by Jan Edelmann, have developed a process that allows lens arrays to be made from glass, enabling them to be mass produced with extreme accur…
A group of researchers at the Fraunhofer Institute, headed by Jan Edelmann, have developed a process that allows lens arrays to be made from glass, enabling them to be mass produced with extreme accuracy, with the possibility of making more conveniently sized projectors possible. Projectors contain lenses that spread the light from the pixilated source in such a way as to illuminate the image area evenly. Until now, this was carried out by means of complicated arrays of lenses placed one behind the other. The same effect has also been achieved recently using flat lens arrays made up of thousands of identical microlenses. This kind of array, which takes up much less space and does not need to be painstakingly assembled and aligned, has, until now been manufactured only from plastic, but the light source in conventional projectors is hot enough to melt them. To solve this problem, the team at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz have developed a process to manufacture lens arrays from glass, during which the surface structure of the array is hot embossed into viscous glass at temperatures of 600-900C. The main challenge is to keep the material exactly at the temperature where it is malleable but not yet molten, said Edelmann. That is the only way to guarantee that components made from it will be within the prescribed tolerances to within a few micrometers. The first step is to produce the forming die equipment, using tungsten carbide which is machined with ultraprecise grinders, and which takes hours to produce. Once it is finished, the die is given a wear-resistant coating of precious metal. Moreover, the glass and the equipment must be kept at a constant temperature until the work-piece has been ejected from the mould during hot embossing as, during the cooling process, the glass shrinks more than the equipment. Tensions would otherwise arise and could cause the lenses to shatter. With regards to handling, the researchers have given the work-piece an edge, also with the highest precision as both stamping dies must be aligned exactly with one another, without any slippage or distortion when pressed together. The team from IWU has succeeded in producing arrays from high refraction glass that have extremely smooth surfaces and where alignment faults are smaller than 20 m. This is a world“s first, said Edelmann. According to the Fraunhofer team, the process is suitable for use in mass production, and could lower the price of these components to a tenth of their current price. These arrays could therefore be used to broaden and homogenize laser beams, for example in industrial welding machines.