Design of compact off-axis three-mirror freeform optical system with small F number

In the field of space optics, the compact freeform optical imaging system with small F number can realize the miniaturization and lightweight of the load, which is beneficial to enhance the ability of target recognition. In this paper, according to the vector aberration theory and the principle of Gaussian brackets, the error evaluation function is constructed by the primary wave aberration coefficients and focal length constraint of the system, and the dynamic weight is used to limit difference in the order of magnitude between various aberrations, which is conducive to rapid convergence in the process of solving the initial structural parameters. In order to achieve the compactness of the system, the circular layout is adopted. The unobstructed initial structure of the off-axis reflective system with conic surfaces is obtained through Particle Swarm Optimization (PSO) algorithm, and the off-axis three-mirror freeform optical system with a highly compact layout is obtained after optimization. In addition, considering the difficulty of freeform surfaces manufacturing, add the manufacturability constraint to the optimization process to control the degree of departure between the aperture edge of the freeform surfaces and the conic surfaces in real time. Compared with the optical system obtained without manufacturability constraints, the difficulty of manufacturing is effectively reduced.