Plastic Coating Developments

Antireflection Coating AR-plas2 for Glass- and Plastic Lenses

Plastic lens with color neutral antireflection coating on right lens part.
© Fraunhofer IOF

Plastic lens with color neutral antireflection coating on right lens part.

There is an increasing demand for high performance antireflection (AR) coatings applied to complexly shaped surfaces. The application of such coatings on strongly curved lenses remains a challenge, particularly when a wide range of light incidence angles is required. PVD deposition processes, commonly used in industry, are not suitable for conformal coating resulting in a shift to shorter wavelength of the antireflection band on inclined areas. Conformal coating deposition has recently been made possible at Fraunhofer IOF using Atomic Layer Deposition pilot plants. This technology is being developed for use in the optics industry; however, it can only partly solve the challenges.

To achieve excellent antireflection properties over the full area of a curved lens with well-established evaporation technology, it is necessary to compensate the spectral shift by widening the AR bandwidth. The crucial factor for minimal remaining reflection is a low effective refractive index n < 1.15 for the final, nanostructured layer. At the same time, requirements for high angles of light incidence can be achieved more easily than before.

Nanostructured surface consisting of Uracil/SiO2.
© Fraunhofer IOF

Nanostructured surface consisting of Uracil/SiO2.

Fraunhofer IOF has identified new organic materials suitable for the generation of nanostructures with refractive indices in a range from 1.08 < n < 1.25. The antireflection coating AR-plas2®, which is based on these materials, can be manufactured cost effectively and on an industrial scale. These multilayer coatings consist of only two to three elements and are distinguished by their excellent environmental stability. On a plastic lens surface, it is possible to etch the first structure directly into the substrate. A nanostructure is formed by etching an organic layer with the use of a patented procedure. This organic structure determines the topography of the subsequently deposited inorganic layer (Fig. 2).

Reflectance of optical lens with antireflection coating AR-plas2.

Reflectance of optical lens with antireflection coating AR-plas2.

After special post-treatments, the final coating contains only residuals of the organic material and is subsequently stable and UV-transparent. These new low-loss coatings allow a color neutral reduction of the reflectance for curved lenses with an average remaining reflectance of < 0.2 % over the visible wavelength range (Fig. 3).

 

 

 

 

Authors: Ulrike Schulz, Peter Munzert, Friedrich Rickelt, Heiko Knopf