Freeform optics design
The unrestricted shape of freeforms has opened the possibility of finding solutions clearly exceeding the performance of their rotationally symmetric counterparts. This applies especially to systems where the specifications (either optical or geometrical) deviate from rotational symmetry. For instance, short throw distance multimedia projectors cannot be placed in front of the center of the projected image without blocking the spectators’ view. This requires the projection to be done from the side. Offset rotational symmetric solutions are not optimal: a freeform projector can improve the image quality on the target area with the same number of surfaces or can match the quality with fewer optical surfaces. Similar problems arise in head-worn displays when trying to make the headsets sleeker while providing excellent image quality. In nonimaging applications, low-beam headlamps of cars also need to produce an asymmetric pattern on the road to avoid blinding the incoming drivers. Freeforms permit to solve these design problems both efficiently and matching aesthetic constraints at the same time.
The continuous progress in the technology to produce and test freeforms, as occurred in the past with rotationally symmetric aspherics, is pushing optical designers to include tailored freeforms in their designs. However, the likewise higher complexity of these unrestricted surfaces introduces multiple new challenges in their design. These challenges range from finding the best mathematical description of the optical surfaces to the design algorithms themselves. In this article, we’ll review a wide range of state-of-the-art freeform design techniques and illustrate their use in specific examples for a wide range of applications.