New Anti-reflective Coating Reduces Reflections

Optical lenses have the task of bundling light. This creates sharp images in cameras, LED car headlights shine brightly and can be controlled flexibly. In order to optimally guide the path of the light rays, complex lens systems are necessary. They consist of several lenses in different shapes. The preferred material for the lenses is now transparent plastic. The cheap injection molding process allows any shape. One problem remains: the reflection of light on the surface of the lenses. The refractive index - a measure of how strongly light is reflected - is around 1.5 for plastic. For comparison: air has a refractive index of 1, so that a lens reflects around 8 percent of the incident light. Curved surfaces reinforce this effect when the light hits at an oblique angle of incidence.

Now researchers from Fraunhofer IOF are presenting a new anti-reflective coating for curved plastic lenses. It reduces the refractive index on the surfaces of the plastic optics to almost 1.1 and thus offers an almost perfect transition to air. The Jena Fraunhofer Institute has already tested prototypes of the layer on various lens systems in close cooperation with industrial partners. The result: the technology significantly reduces so-called false light. False lights are reflections that, for example, ghost around in lens systems of cameras and disrupt the bundling of light rays. The researchers were also able to prove in their experiments that lenses coated with the IOF anti-reflective coating allow significantly more light to pass through than conventional lenses.

The Jena scientists' anti-reflection system combines several new nanostructured layers with the previously used homogeneous oxide layers - stacked on top of each other. With each layer, the researchers dilute the plastic more with air. Until the refractive index of the surface almost corresponds to that of the air. They do this by using new nanomaterials that they can apply to complex shaped lenses. Stacking several layers enables them to make the anti-reflective coating twice as thick as previous solutions. Conventional anti-reflective coatings can only be distributed unevenly on curved lenses: the edge becomes thinner at the edge than in the curved center. (qui)

K 2016: Hall 7.0, Stand SC01