Variable optical filters for enhanced image sensor performance

Image sensors today are more and more used in all kinds of research applications like outer space or aviation. Especially in outer space applications it is essential to have reliable and good quality cameras that can dynamically adapt to different situations (Fig.2). In the scope of a Fraunhofer IIS internal research project we are trying to establish a new approach in sensor design, where pixelwise adjustable optical filters in front of the imagesensor allow for achieving significant improvements in terms of dynamic range, color space or spectrum. Liquidcrystal technology gives a lot of opportunities to realize arrays of filter cells, where every filter cell can be controlled individually. Similar panels are already used in LCD beamers. The pixel size is about 5 μm and the process of manufacturing is compatible with CMOS image sensor manufacturing. With liquid crystal technology it is possible to design filters with very diverse characteristics. The amount of transmitted light can be controlled as well as the transmitted spectrum. Even polarization can be regulated. First experiments with custom liquid crystal filters and a simple demonstrator are promising and we expect to be able to extend the dynamic range of actual cameras from 60-70 dB to more than 110 dB by using this technology.