Transmission volume holograms for LED illumination

The application of transmission holograms in automotive headlamp systems is a possible new field of application for holographic elements. However, it requires the adaptation of holograms to light-emitting diodes (LEDs) as reconstruction light sources. This includes the consideration of the reconstruction wavefront shape. Therefore, computer-generated holograms (CGHs) are designed for different LED wavefront approximations and recorded in a photopolymer. Within experiments, the performance of the optimization is analyzed. For reconstruction, an automotive-certified LED is used and the reconstructed image is recorded. The correlation of the ideal and the real reconstructed image is used as indicator for a successful adaptation within the design process. It is shown that there are clear differences regarding the improvement of the correlation between the considered wavefront approximations. The best results are achieved with a wavefront, determined from an interferometric measurement, and with a wavefront with Lambertian characteristic

Holograms in automotive headlamps - chances and challenges

Holograms provide the possibility to modulate incident light waves in an almost arbitrary way. This leads to the idea to use holograms as supplementing or replacing element in the optical system of automotive headlamps. In this paper one important aspect, the efficiency of a volume hologram, is discussed regarding conditions of automotive headlamps

Design and simulation of computer-generated volume holograms for automotive headlamps

The application of holograms as light shaping elements in automotive headlamps requires the adaption of the holographic information to the characteristics of the reconstruction light source. This paper shows first results regarding the adaption to different wavelengths for realizing a white light distribution by illuminating a hologram with a white light emitting light source

Optimization of computer-generated transmission holograms using different LED wavefront approximations

The reconstruction of computer-generated transmission volume holograms with light-emitting diodes (LEDs) requires the adaptation of the holograms to the specific diodes' wavefronts. We show first results of the analysis of different LED wavefront approximations, including a new interferometry-based approach to measure an LED wavefront

Möglichkeiten und Grenzen der interferenzlithografischen Herstellung modulierter Blazegitter

Interferenzlitographisch hergestellte holographisch-optische Bauelemente (HOEs) stellen eine leistungsfähige Alternative zu beugungsoptischen Bauelementen dar, die mit klassischen lithographischen Verfahren hergestellt werden. Eine generelle Problemstellung ist dabei die Anpassung der beugenden Strukturen an eine bestimmte Anwendungswellenlänge. Oft besteht jedoch auch der Anspruch, derartige Elemente für mehrere Wellenlängen oder, wie z.B. in der Spektralsensorik, für größere spektrale Bandbreiten auszulegen. Zur Beeinflussung bzw. Umverteilung der spektralen Effizienzcharakteristik ist die gezielte Modulation der Profilform (Höhenvariation, Blazewinkel) über das gesamte Element anwendbar. Technologische Herausforderung ist dabei die Generierung einer modulierten Resistmaske bereits im holografischen Prozess. Wir diskutieren die Profilentstehung an Hand eigener Simulationsrechnungen zur Resiststrukturierung mit gegenläufigen Wellen sowie experimentell gewonnener Daten. Das nutzbare Prozessfenster, innerhalb dessen sich effiziente Blazestrukturen mit lokal variierender Tiefe bei unverändertem Interferenzfeld generieren lassen, wird dabei abgeleitet

Imaging gratings with modulated blaze - realized by a combination of holography and reactive ion beam etching

Blazed gratings are in general the best choice for achieving the maximal diffraction efficiencies in a moderate wide wavelength band. However, a number of applications such as typical spectrometer systems need a broader spectral range. Here the drop of diffraction efficiency for the employed order towards the edges of the addressed spectrum limits the dynamics of the spectral sensor system. Thus we present a systematic approach based on a combination of interference lithography and ion beam etching. It provides a tuneable spectral response curve even for imaging gratings by mixing the characteristics of different blazed angles without influencing the systems spectral resolution