Process
Process
Mask structured ion exchange (MSI)
The manufacturing process is the silver-sodium ion exchange in planar optical glass. The ion exchange is carried out thermally or with field support at temperatures around 500 ° C.
The replacement of the sodium ions originally contained in the glass with silver ions from a molten salt leads to an increase of the optical refractive index. This effect is used to design optical functions. Other physical and optical properties of the glass do not change, however.
With the help of a photolithographically structured metal mask, the ion input and thus the index distribution within the glass can be controlled locally.
This makes it possible to generate optical functions in the glass with high precision. Step-free, continuous refractive elements are created.
After the replacement process, the metal mask is completely removed. The optical function is given solely by the index distribution within the glass.
Advantage:
the surfaces remain flat. They are therefore easy to clean.
Reflections can be effectively suppressed by index matching or by an AR coating.
The process allows high precision in the generation of specified phase profiles as well as the best reproducibility.
Interferometrically controlled laser lithography system DWL66 from Heidelberg Instruments with a writing wavelength of 405nm.
Section from a mask structure for the production of a microlens array. The individual miro lenses in this example have an edge length of 600 µm in a Cartesian arrangement. The mask consists of several thousand punctiform mask openings per lens. The ion exchange is controlled locally by the density and size of the openings.