TR2020-183

Design of freeforms to uniformly illuminate polygonal targets from extended sources via edge ray mapping


    •  Birch, D.A., Brand, M.E., "Design of freeforms to uniformly illuminate polygonal targets from extended sources via edge ray mapping", Applied Optics, DOI: 10.1364/​AO.392193, Vol. 59, No. 22, pp. 6490-6496, August 2020.
      BibTeX TR2020-183 PDF
      • @article{Birch2020aug,
      • author = {Birch, Daniel A. and Brand, Matthew E.},
      • title = {Design of freeforms to uniformly illuminate polygonal targets from extended sources via edge ray mapping},
      • journal = {Applied Optics},
      • year = 2020,
      • volume = 59,
      • number = 22,
      • pages = {6490--6496},
      • month = aug,
      • doi = {10.1364/AO.392193},
      • url = {https://www.merl.com/publications/TR2020-183}
      • }
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  • Research Area:

    Applied Physics

Abstract:

We consider the design of a compact freeform optical surface that uniformly irradiates an arbitrary convex polygonal region from an extended light source while controlling spill. This problem has attracted a large literature, mainly treating highly symmetric special cases or cases where the solution is approximated by a zero-├ętendue design based on a point source. Practical versions of this illumination design problem will likely feature large asymmetric LEDs, compact lenses, and irregular targets on angled projection surfaces. For these settings, we develop a solution method based on an edge ray mapping that routes maximally off-axis rays from the edges of the source through the edge of the optic to the edges of the target polygon. This determines the sag and normals along the boundary of the freeform surface. A "spill-free" surface is then interpolated from the boundary information, and optimized to uniformize the irradiance while preserving the polygonal boundary. Highly uniform irradiances (relative standard deviation < .01) can be attained with good control of spill, even when the exit surface is < 3 source diameters from the embedded source.