Simulation and design of a Fresnelized freeform optic for a head-up display

Freeform optics are used to create complex application-adapted illuminance distributions due to their high number of adjustable degrees of freedom. As with conventional optics, this can result for some applications in large optics that exceed the available installation space or lead to high production costs. While the use of Fresnel lenses is common in such cases for conventional optics, the Fresnelization step in the design process of freeform optics is more complex due to the lack of rotational symmetry and only done for specific cases. Therefore, this paper presents a method to examine different segmentation strategies on freeform lenses and to optimize Fresnelization parameters. In this work, the method will be demonstrated using a head-up display (HUD) as example, in which the combination of a Fresnel lens and a display creates a moire pattern in the illuminance distribution. In order to accelerate the simulation of complex Fresnel freeform optics considerably, a special ray tracing algorithm is developed, which takes advantage of the segmentation characteristics. The simulation approach of the illuminance distribution and the optimization of the Fresnelization are shown and discussed on a lens with about 300 segments visibly reducing the moire pattern.