Design Of Off - Axis Reflective Optical System For Free - Form Surface

As the manufacturing technology matures day by day, optical freeform surface is widely applied to the optical system design for better system performance and simplified system structure due to its multi-degree of freedom and strong aberration correction ability. The reflective optical system also has lots of advantages. Applying the freeform surface to the reflective system makes the design of off-axis system with wide field of view and low F number possible.In this thesis, the optical design of off-axis reflective system with freeform surface was studied. By adopting progressively approximation optimization method and combining strategies of surface shape and field of view (FOV) optimization, an off-axis reflective two-mirror system with freeform surface of polynomial XY was designed. The entire system has a compact structure. Its focal length is 440 mm; the diameter of the entrance pupil is 88 mm; the FOV is 2°×2°; the spot radius is less than 20μm, namely, the pixel size of the selected CCD (charge coupled device). The modulation transfer function (MTF) at 30 line pairs/mm is larger than 0.5. In addition, based on the technical indicators of the off-axis reflective system with two-mirror, an off-axis reflective three-mirror system with the exact same surface and further expanded FOV was designed by adopting the Zemax macro language program structural-constraining method, the F number of which is 5 and the FOV is 20°×10°. The imaging quality of this system is close to the diffraction limit. Last but not the least, the alignment of the off-axis three-mirror system was simulated by Zemax. The offset compensation relationship between the tilt and decentration of a single optical element and also of multiple ones was analyzed in order to direct the system alignment process.