Coatings for Highly Curved Lenses

A strongly curved glass lens, half-side AR-coated (Source: Fh.-IOF)

A strongly curved glass lens, half-side AR-coated (Source: Fh.-IOF)

The market for optical components has been growing over the past years – that is the reason why antireflective structures have been of high technical importance as well. Those are indispensable to avoid low luminous efficacy, loss of contrasts in images, and ghost images, which are generated by uncontrolled reflections of light. An association of researchers from science and industry, coordinated by Carl Zeiss Jena, has developed an antireflective method in the recently completed FIONA project (Colorless interference layers for antireflection by using organic nanostructure). These coatings work in a significantly broader spectral range and can be applied on the surface of strongly curved lenses.

According to a recent study by Markets&Markets, optical coatings have generated an annual turnover of roughly 1.02 billion dollars (2014) with a predicted growth rate of 8.4 percent up to 2020. These numbers underline the growing importance of broad-band AR-coatings for complex surfaces in the optics manufacturing.

An ideal AR-coating has a gradual refractive index transition between the surface of the substrate and the surrounding medium air. That is why antireflection properties can be improved by using a low-index material for the interference systems on the outer layer. Nanostructures with a size smaller than the wavelength of light can act like such a low-index coating. Therefore, the aim of the project was to develop a method for the fabrication of antireflection coatings via nanostructured layers. The resulting layer systems feature innovative combinations of classical optical interference coatings with such nanostructures. The so-called sub-wavelength structures with a thickness of less than one hundred nanometers have been generated through different methods. At the Fraunhofer IOF, the established method of plasma structuring “AR-Plas” has been applied to new organic layers, whereas Carl Zeiss Jena has focused on inorganic nanostructured silicon dioxide and magnesium fluoride.

The newly developed coatings are world-leading in their ability to work on highly curved lenses. The widened angular acceptance of the antireflection coatings, their homogeneous properties on strongly curved surfaces, as well as the AR-effect on significantly broader spectral ranges are of particular note in this context. The obtained AR-effect extends from the visual into the infrared spectral range and is colorless even in case of strongly curved lenses. A residual average reflectance below 0.3 percent was achieved in the spectral range from 400 nm to 1500 nm, which is significantly lower than with classical AR-coatings. The method has been found suitable for a multitude of optical components e.g. optical lenses for cameras, microscopes and medical technology devices. The project partners’ demonstrator lenses do reveal the optimized AR effect and enhanced optical properties.

Project partners were: Agfa-Gevaert Health Care GmbH, asphericon GmbH, Carl Zeiss Jena GmbH, Leica Microsystems GmbH and Qioptiq Photonics GmbH & Co. KG.(Source: Fh.-IOF)

Link: Fraunhofer Institute for Applied Optics and Precision Engineering, Jena, Germany

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