Freeform Fresnel lenses with a low number of discontinuities for tailored illumination applications.

Most work in the field of freeform lens design has been focused on finding design algorithms for continuous freeform lens surfaces which transform an arbitrary ingoing light distribution into an arbitrary outgoing distribution. The shape of the resulting continuous lens surfaces depends fully on the source and target light distribution for which the lenses are tailored. In some cases this results in large, voluminous optical components which depending on the application are not practical. Fresnel lenses can have a much smaller volume, but are not straightforward to design in the case of freeform lenses. This paper demonstrates a new method to design freeform Fresnel lenses based on concentric freeform segments. Such lenses have a much lower number of discontinuities compared to already existing Fresnel-type freeform lenses which are based on an array of facets. Less discontinuities means less stray light due to the unavoidable rounding errors with current manufacturing processes. The new design method is first explained, and then illustrated for a freeform Fresnel lens with a rectangular target distribution in the far-field.