Variable microstructured optics

Microstructured optical elements are used in a variety of technical devices. Optical gratings are used for colour separation in spectroscopes, holograms and microlens arrays and are used for the energetic beam shaping of lasers. Even in the field of imaging and illumination there are possibilities for beam guidance, e.g. with diffractive lenses.

The variable micro-optics project is investigating whether such conventional micro-optical components can be transferred to variable elements without sacrificing optical performance. This would make it possible to develop actively controlled systems that contain components such as a diffractive lens with a tunable focal length or a grating in which the angle of spectral decomposition can be adjusted as an essential basis. The variable functionality is to be achieved by controlled lateral deformation of a plane-parallel elastomer carrier on which a microstructure is imprinted [Fig. 1].

The fields of investigation include the mechanical and optical simulation of the variable elements as well as the technical realisation, which is divided into the moulding of the elastic optics, the development of a constructive solution for various stretching processes and the topographical and optical inspection of the effective surfaces.

Initial results have already been achieved in the field of combined optomechanical simulation. For example, "Ansys", a commercial finite element programme, is used to calculate the strain of microstructured elastomer elements on the basis of non-linear material parameters [Fig. 2].

The resulting structural deformation serves as the basis for the wave-optical calculation of the diffraction using the Unigit software, which uses the mathematical model of rigorous coupled-wave analysis (RCWA) for the calculation. This networked simulation from the fields of mechanics and optics enables an exact prediction of the light distribution of the variable elements depending on the different strain states. Subsequently, e.g. dependencies on other optically relevant influencing variables can be visualised [Fig. 3] in order to open up the possibilities of using such elements.