Bösel Christoph, Gross Herbert
Appl Opt. 2019 Apr 1;58(10):2713-2724. doi: 10.1364/AO.58.002713.
One of the major problems in freeform illumination design in a geometrical optics approximation is picture generation with extended light sources. In contrast to the freeform design with zero-étendue sources, the extension of the light source leads to the typical blurring effect and a contrast reduction of the required irradiance. This effect can be minimized by increasing the distance between the freeform surface and the light source, which according to étendue conservation, results in an impractically large projection optic. To tackle this problem, we propose a design concept consisting of the combination of a pattern-generating double freeform surface for collimated beam shaping, which is calculated for a zero-étendue light source, and an imaging projection system with a telecentric object space. The design concept works independently of the shape of the emission area of the light source and does not require a representation of the extended light source by several individual wavefronts. By interpreting the pattern blurring effect as a composition of a shift contribution and a distortion contribution, we show that both can be minimized simultaneously by an appropriate placement of the object plane of the imaging optics and by making the distance between both freeform surfaces as small as possible. This allows the calculation of compact, energy-efficient freeform illumination systems for picture generation with real extended light sources. We demonstrate the significant blurring reduction by designing a simple illumination system consisting of a collimation optic, a (zero-étendue) double freeform lens for collimated beam shaping, and a projection lens for the generation of the target distribution "Elaine" with an extended Lambertian emitter of 3 ×3 extension and ±42 maximum opening angle. For a working distance to the projection system of 500 mm and a target area of 300 ×300 , a relative blurring extension of 2% is estimated, compared to 23% for a single freeform projector with the same energy throughput and similar lateral extension. The influence of the doublefreeform thickness on the blurring reduction is demonstrated, and a summary of the design procedure for the developed design concept is given.
几何光学近似下自由形式照明设计中的一个主要问题是使用扩展光源生成图像。与使用零 étendue 光源的自由形式设计不同，光源的扩展会导致典型的模糊效应以及所需辐照度的对比度降低。通过增加自由形式表面与光源之间的距离，可以将这种效应最小化，但根据 étendue 守恒，这会导致投影光学器件尺寸过大而不实用。为了解决这个问题，我们提出了一种设计概念，它由一个用于准直光束整形的图案生成双自由形式表面（针对零 étendue 光源计算）和一个具有远心物空间的成像投影系统组合而成。该设计概念与光源发射区域的形状无关，并且不需要用几个单独的波前来表示扩展光源。通过将图案模糊效应解释为偏移贡献和失真贡献的组合，我们表明通过适当地放置成像光学器件的物平面并使两个自由形式表面之间的距离尽可能小，可以同时将两者最小化。这使得能够计算出紧凑、节能的自由形式照明系统，用于使用实际扩展光源生成图像。我们通过设计一个简单的照明系统来证明显著的模糊减少，该系统由一个准直光学器件、一个用于准直光束整形的（零 étendue）双自由形式透镜以及一个用于生成目标分布“Elaine”的投影透镜组成，该系统使用一个 3×3 扩展且最大开口角为±42°的扩展朗伯发射体。对于到投影系统的 500 毫米工作距离和 300×300 的目标区域，估计相对模糊扩展为 2%，而对于具有相同能量通量和类似横向扩展的单个自由形式投影仪，这一数值为 23%。展示了双自由形式厚度对模糊减少的影响，并给出了所开发设计概念的设计过程总结。
