Dr. Chen Li Profile

Dr. Chen Li

at Fraunhofer-IOF

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Author

Publications (6)

Proceedings Article | 21 June 2019 Presentation + Paper

Enhanced field-of-view structured illumination projector using stacked microlens arrays

Rohan Kundu, Peter Schreiber, Peter Dannberg, Stephanie Fischer, Chen Li, Uwe Zeitner, Andreas Tünnermann

Proceedings Volume 11062, 110620Y (2019) https://doi.org/10.1117/12.2525813

KEYWORDS: Projection systems, Light emitting diodes, Micro optics, Lenses, Computer aided design, Microlens array, Optical design, Manufacturing, Monochromatic aberrations, Optical lithography

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Proceedings Article | 28 May 2018 Paper

Etendue conserving light shaping using microlens arrays with irregular lenslets

Chen Li, Peter Schreiber, Dirk Michaelis, Christoph Wächter, Stephanie Fischer, Uwe Zeitner

Proceedings Volume 10693, 1069304 (2018) https://doi.org/10.1117/12.2313803

KEYWORDS: Beam shaping, Lens design, Microlens array, Grayscale lithography, Diffusers, Beam homogenizers

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Proceedings Article | 23 September 2015 Paper

Freeform array projection

D. Michaelis, P. Schreiber, C. Li, A. Bräuer, H. Gross

Proceedings Volume 9629, 962909 (2015) https://doi.org/10.1117/12.2191221

KEYWORDS: Collimation, Projection systems, Light, Cones, Freeform optics, Channel projecting optics, Image segmentation, Optical components, Homogenization, Eye

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Proceedings Article | 23 September 2015 Paper

Mapping algorithm for freeform construction using non-ideal light sources

Chen Li, D. Michaelis, P. Schreiber, L. Dick, A. Bräuer

Proceedings Volume 9629, 96290E (2015) https://doi.org/10.1117/12.2191207

KEYWORDS: Freeform optics, Light emitting diodes, Matrices, Chemical elements, Optical components, Detection and tracking algorithms, Light, Optical systems, Optimization (mathematics), Light sources

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Using conventional mapping algorithms for the construction of illumination freeform optics’ arbitrary target pattern can be obtained for idealized sources, e.g. collimated light or point sources. Each freeform surface element generates an image point at the target and the light intensity of an image point is corresponding to the area of the freeform surface element who generates the image point.

For sources with a pronounced extension and ray divergence, e.g. an LED with a small source-freeform-distance, the image points are blurred and the blurred patterns might be different between different points. Besides, due to Fresnel losses and vignetting, the relationship between light intensity of image points and area of freeform surface elements becomes complicated. These individual light distributions of each freeform element are taken into account in a mapping algorithm. To this end the method of steepest decent procedures are used to adapt the mapping goal. A structured target pattern for a optics system with an ideal source is computed applying corresponding linear optimization matrices. Special weighting factor and smoothing factor are included in the procedures to achieve certain edge conditions and to ensure the manufacturability of the freefrom surface. The corresponding linear optimization matrices, which are the lighting distribution patterns of each of the freeform surface elements, are gained by conventional raytracing with a realistic source. Nontrivial source geometries, like LED-irregularities due to bonding or source fine structures, and a complex ray divergence behavior can be easily considered. Additionally, Fresnel losses, vignetting and even stray light are taken into account. After optimization iterations, with a realistic source, the initial mapping goal can be achieved by the optics system providing a structured target pattern with an ideal source.

The algorithm is applied to several design examples. A few simple tasks are presented to discussed the ability and limitation of the this mothed. It is also presented that a homogeneous LED-illumination system design, in where, with a strongly tilted incident direction, a homogeneous distribution is achieved with a rather compact optics system and short working distance applying a relatively large LED source. It is shown that the lighting distribution patterns from the freeform surface elements can be significantly different from the others. The generation of a structured target pattern, applying weighting factor and smoothing factor, are discussed. Finally, freeform designs for much more complex sources like clusters of LED-sources are presented.

Proceedings Article | 24 September 2011 Paper

Freeform reflector design for LED street lighting

Chen Li, Peter Schreiber, Andreas Walkling, Christoph Schierz, Maik Schwede, Volker Gühne

Proceedings Volume 8123, 81230O (2011) https://doi.org/10.1117/12.893602

KEYWORDS: Roads, Light emitting diodes, Lamps, Reflectors, Light sources and illumination, Reflector design, Reflection, Stray light, Manufacturing, LED lighting

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Proceedings Article | 21 September 2011 Paper

Construction of freeforms in illumination systems via generalized Cartesian oval representation

D. Michaelis, P. Schreiber, Chen Li, A. Bräuer

Proceedings Volume 8124, 812403 (2011) https://doi.org/10.1117/12.893564

KEYWORDS: Cobalt, Geometrical optics, Radon, Freeform optics, Optical components, Ray tracing, Collimation, Prisms, Light, Wavefronts

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Showing 5 of 6 publications

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