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

In this study, we propose an effective design method for a compact freeform <i>f</i>-<i>θ</i> 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 <i>f</i>-<i>θ</i> 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<i>m</i><i>m</i> 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.