Schott believes glass beats plastic

13 Aug 2007

Modern optical systems could benefit from a new method that allows diffractive optical elements to be made from glass instead of plastic.

Glass DOEs

A new pressing technique is helping German company Schott to mass produce diffractive optical elements (DOEs) from glass for the first time. Exhibiting a high diffraction efficiency of up to 95 %, the glass DOEs are said to offer better material properties compared with conventional plastic DOEs.

"Glass DOEs overcome all of the weaknesses of polymers which suffer from high scattering losses, low resistance to temperature, moisture, laser and chemicals," Helge Vogt, New Products Manager at Schott, told optics.org. "Modern optical designs require different glass types to achieve best optical performance. Our precision glass DOEs can be made out of various optical glasses, which means we can offer much better flexibility."

Until now, the majority of mass produced DOEs could only be manufactured from plastic or fused silica glass which requires expensive lithography techniques and etching processes.

"We are able to offer a large variety of optical glasses for DOE production. One key property of a glass DOE is that several optical functions can share the same substrate and therefore have the ability to reduce the weight of an optical system," added Vogt. "What's more, our pressing technique means that there is also the potential for large-scale production."

Schott says it can produce a variety of DOEs such as Fresnel zone lenses, blazed gratings and computer-generated holograms using its precision glass molding process. "This process technology requires special glass, called low transformation temperature (Tg) optical glass," explained Vogt. "In the process, a low-Tg optical glass preform is inserted into a mold that consists of the surface pattern for the DOE. It is then heated to a sufficiently low viscosity before being pressed into its shape."

The low-Tg optical glass exhibits transformation temperatures below 550 °C which helps to increase the lifetime of the molds and to reduce process time.

The DOEs diffract light and bundle it into beams with exact shapes and in the desired direction. "DOEs represent the key to miniaturization of optical systems," concluded Vogt. "They can serve as a replacement for refractive lenses as well as corrective optical elements for compensation of aberrations."

The new DOEs are available now and can be made to specification by Schott.