A high-throughput framework from design to fabrication of freeform diffractive optical elements for beam shaping

Abstract

Freeform diffractive optical elements (DOEs) for beam shaping that generates a specific laser beam profile on the work surface have great demand in projectors, sensing, metrology, optical communication, automotive lighting, HUD and so on. However, tailoring the generated phase continuous and regular with better high-volume manufacturability and reduced light scattering losses is still a big challenge since traditional design tends to stagnate at local minima with slow convergence and fabrication of irregular microreliefs stays at experimental level. Here, a high-throughput approach to producing low-cost freeform DOEs from design to fabrication is proposed. A continuous freeform lens with regular DOE microreliefs was designed using a differentiable multi-level B-splines method [1]to efficiently control the light and generate a refined 41.9 mm × 41.9 mm image. Then, mold for freeform lens fabrication is machined by slow tool servo (STS) process, whose tool path is generated by equal arc length method to ensure the surface quality and process accuracy. Finally, PMMA freeform lenses can be achieved by precision compression molding process. Furthermore, characterizations of surface morphology and optical performance confirmed that the molded lens has satisfied optical surface, geometric shape and expected beam shaping effect. The proposed design-to-fabrication framework in this work provides a feasible technical path for mass production of high precision freeform DOEs and will significantly promote the widespread applications of all freeform optics.