Optical design of a freeform f-θ lens for the 405 nm laser scanning unit

In this study, we propose an effective design method for a compact freeform f -θ lens system for 3D printing laser scanning units. A two-phase design strategy based on surface-type upgrade is put forward for the design of the f -θ lens, where different models and design targets are adopted at different stages in optimization. An automatic linearity error correction procedure is proposed to replace the tedious manual adjusting process. A design result comparable with the A4 scanning width was obtained following the proposed design strategy. The relative difference in diffraction spot size is below 3.05% in ±100 mm scanning width, and the linearity error stays below 0.3%, indicating a good optical performance. The tolerance performance and thermal analysis show that the design result meets the requirement in real usage conditions.