Optimization of computer generated transmission holograms using LED wave front approximations

The overall aim of this project is the application of holograms in illumination systems of automotive headlamps with LED illumination. To get a reconstructed image with good quality, the parameters of used LEDs have to be considered within the design process of the holograms. Two important parameters are the high divergence angles and the dimensions of the light emitting surface. To avoid the usage of additional optical components, the holograms should be optimized for the reconstruction with divergent light emitted from a certain area. Therefore, a precise description of the emitted light distribution is necessary. Within different test series the light wave emitted by a LED is approximated in different ways, e.g. as an ideal spherical wave or as superposition of several spherical waves. In addition, the emitted waves are calculated using measurements with an interferometer and phase retrieval algorithms. The holograms are calculated for maximum divergence angles of ±4°, due to limitations of the labor setups, exposed in a photopolymer and reconstructed with a LED. The quality of each reconstructed image is analyzed to get an impression of the usefulness of the LED approximations.