In a study published in Optics Letters, Prof. MENG Qingyu and his Doctoral student QIN Zichang from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of Chinese Academy of Sciences (CAS) proposed a desensitization design method for freeform optical system based on local-curve-control, which can effectively reduce the error sensitivity of freeform optical systems.

Freeform surface, with its super high degree of freedom, performs well in aberration correction of asymmetric aberration, and has been applied in many fields. However, most of the current research is still focused on how to improve the imaging quality of optical systems by using freeform surfaces, without considering the as-built performance.

Error sensitivity is an important index to measure whether an optical system can be realized from theoretical design. Therefore, how to reduce the error sensitivity of the optical system while ensuring the imaging quality of the freeform optical system is an urgent problem to be solved.

Based on the idea of differentiation and pupil sampling, the complex freeform surface was divided into several simple quadric surfaces, and the curvature of each local area was controlled, so as to evaluate and optimize the error sensitivity of the optical system of freeform surface.

With a focal length of 850 mm, F number 4.25, field of view (FOV) of 20°×30°, the off-axis three-mirror optical system was taken as an example to optimize the design of desensitization. Through the Monte Carlo tolerance analysis method, compared with the traditional design method and Zemax OpticStudio’s built-in “TOLR” method, the results obtained by desensitization design method proposed by the research team had less Δ wavefront error (WE) and shorter optimization time under the same error conditions, which verifies the correctness of the research content and the effectiveness of the desensitization design method.

The desensitization design method of freeform surface optical system based on local curvature proposed by the researchers can not only ensure the imaging quality of freeform surface optical system, but also reduce the error sensitivity of optical system and improve the ability of optical system to resist error interference. This provides a powerful help for the realization of freeform surface imaging optical system with large FOV.