| 摘要 |
A two-element f-theta lens used for a micro-electro mechanical system (MEMS) laser scanning unit includes a first lens and a second lens, both in a meniscus shape having a concave surface facing the side of the MEMS reflecting mirror. The two-element f-theta lens comprising a first lens with a first optical surface and a second optical surface and a second lens with a third optical surface and a fourth optical surface, both in a meniscus shape and having a concave surface on the side of the MEMS reflecting mirror; at least one optical surface is aspherical surface in both main scanning direction and sub scanning direction, and satisfies specifical optical conditions. The two-element f-theta lens corrects the nonlinear relationship between scanned angle and the time into the linear relationship between the image spot distances and the time. Meanwhile, the two-element f-theta lens focuses the scan light to the target in the main scanning and sun scanning directions, such that the purpose of the scanning linearity effect and the high resolution scanning can be achieved.
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