Freeform illumination lens design using composite ray mapping

We develop a new ray mapping approach to address the surface error and hot spot issues in designing a freeform total internal reflection (TIR) lens for nonrotational uniform illumination. Our proposed ray mapping approach partitions the source intensity distribution in the peripheral regions using the traditional spherical coordinate system to design the freeform TIR surfaces and in the central regions using the modified spherical coordinate system to design the freeform refractive surface. This new design method will reduce the surface error in the current ray mapping methods, therefore improving the illumination uniformity significantly. In addition, the freeform lens designed with this approach is much more robust than the lenses designed using other ray mapping methods.