Advanced printer for volume holographic optical elements in automotive exterior lighting

Abstract

Volume holographic optical elements (vHOES) are currently used in various applications, like augmented reality displays or wearables. Yet, the use of vHOEs as illumination optics has not found its way into products. In automotive exterior lighting vHOEs could enable unique styling, reduction of installation space, weight, and material. However, in headlamps, rear lamps, or signal lamps, several technical and conceptional challenges must be addressed. One of these challenges is to replace lasers, which are expensive and have high safety demands, by light emitting diodes (LEDs), which are widely used in the field of automotive lighting. The reconstruction of volume holograms with LEDs is straightforward for graphical holograms showing a three-dimensional scene. For automotive exterior lighting, however the hologram is not just a design element, but in addition must feature a light distribution fulfilling all the legal requirements. The vHOE thus becomes the most important functional element of the lighting system. For instance, the low beam distribution must provide a sharp, asymmetric cutoff line and white color, which turns out to be difficult. We have developed an improved manufacturing technique of such vHOEs, using two spatial light modulators (SLMs). In this paper we present the design, the holographic printer setup, and first experimental results of vHOE samples.