Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings can be flexibly adapted to different wavelengths. To generate an effective (> 99 %) light absorption of an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer’s material. On this basis, different black absorber coatings were developed and deposited on optical components for actual applications. A wideband black absorber for 400 -1000 nm wavelength on a space spectrometer slit, a bi-directional black coating for a single wavelength in the VIS, which can be wet-chemically etched for micro-patterning, and a black aperture for NIR and SWIR light on the exit face of a dispersion prism are presented.
Recently the first automotive vehicles with micro-optical headlights entered the market as series production models. Besides aesthetics, multi aperture micro-optics bring the advantage of a reduced axial length of the system due to the much shorter focal length of each channel. However, the currently implemented low-beam systems suffer from low transmission and notable cost for the micro-optics elements. Both problems can be traced back to the buried micro-slides within the micro lens arrays, (MLA) which shape the distribution. To overcome these issues, we developed a micro-optical solution for a low-beam without mask layers, thereby significantly increasing transmission to a very competitive level and enabling more cost-effective manufacturing processes. Our design follows the general principle of a fly’s eye condenser (FEC) but comprises of a multitude of differently shaped lenslets, which form the beam collectively. The design process includes the generation of the overall distribution as well as detailed features such as the sharp and specially shaped cut-off and a smooth distribution within the beam. Particular effort is necessary to control stray light which is caused by imperfect manufacturing of the MLAs. A first LED-illuminated demonstrator showed that the shape and the required sharpness of the cut-off can be achieved even without the use of absorbing masks with a single optical module. Stray light control and fine tuning of the distribution makes it possible to manufacture a maskless polymer-on-glass micro-optical component and generate a beam pattern in accordance with UNECE safety regulations.
The monitoring of anthropogenic CO2 by satellites (part of Copernicus, the European Union’s Earth Observation and Monitoring program) requires a special dispersive spectrometer. As a highly efficient light dispersing element, a Prism-Grating Prism (PG-P) optical element will operate in the program, mentioned above. Anti-reflection (AR) coatings and light blocking apertures are requested to suppress optical losses, to reduce stray light and to shape the beam. Beside the AR-coatings, deposition of “black” aperture as a coating directly on the PG-P element, allows to abstain a mechanical aperture. Thereby, reduced number of elements in the optical setup and therefore reduced payload of the satellite can be achieved. For this purpose, an antireflective coating inside a clear aperture combined with a light blocking and absorbing aperture-coating outside the clear aperture was realized. The developments shown in this contribution were performed for the application wavelength of 1590 - 1675 nm.
Micro-optical array projectors are discussed as replacement for structured illumination in applications with critical space requirements. The concept bases on the fly’s eye condenser principle and a well-defined buried array of micro-dia. Their optical performance benefits from etendue conservation and the large depth of field of applied short focal lenses. As an established technique to generate microlens profiles, thermal reflow of binary patterned photoresist is known for more than three decades. This approach leads to lens arrays with filling factors up to ~90% when used in hexagonal arrangement. Further increment requires direct writing methods such as grayscale lithography. Recently a LED based projection stepper-like lithography system became competitive, because it allows structure depths beyond 50 microns. It utilizes an LCoS micro-imager as variable 8-bit reticle and a high dynamic dosage controlled illumination. This paper represents the evaluation of the technique for the generation of refractive lens profiles by means of metrology and optical performance of micro-optical array projectors. Micro-array projectors based on circular lenslets will be compared, followed by the analysis of closely packed square-shaped lenslets. The aim is to understand the impact of lens shape deviation, conical constant or statistical distribution of lens properties like sag height, radius of curvature on the projection. A correlation of imperfections and quality loss due to scattering, aberrations, and mismatch of images in the overlay of different projectorlets will be given. The work concludes with an outlook on further developments in mastering micro-optical profiles for illumination application.
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