Design Of Imaging System Based On Optical Free-form Surface

The optical elements used in traditional optical imaging systems are usually plane or spherical.In order to satisfy certain imaging effects,multiple elements are usually needed to compensate for optical aberrations,which results in complexity and heaviness of optical systems.Compared with the traditional imaging system,the free-form optical elements have more degrees of freedom and special object-image mapping relationship.Thus the imaging quality of the optical systems using free-form surfaces is always superior to the traditional ones especially on the elimination of off-axis aberrations such ascoma aberration,astigmatism,field curvature.In this thesis,arefractive imaging systemis designed as an example to greatly reduce aberrations using free-form surfaces.The main tasks are as follows:1.Investigate the existing optical free-form surface products,and clarify the development of optical free-form surface and the current achievements.2.The design methods and mathematical expressions of several kinds of optical free-form surfaces are introduced in detail to provide theoretical guidance for the later design.3.A novel algorithm based on Point-by-point algorithm and Fermat’s theorem for solving the free-form surface is proposed.This algorithm is realized in MATLAB to obtain the feature points,which are fitted to the free-form surface with least squares algorithm.4.This novel algorithm can be used to design a system with the point spread function of any shape.The simulation results show that the MTF(modulation transfer function)curves are close to the diffraction limit.The design of refractive optical systems usually adopts traditional surface shapes,which are usually rotationally symmetrical.In the actual design process,off-axis aberrations are always introduced,which is inevitable.However,free-form surfaces can reduce off-axis aberrations because of their multiple degrees of freedom.This thesis extends the design method of the free-form surface based on Point-by-point algorithm from reflective systems to refractive systems.This method can be applied to design a system with arbitrary point spread functions.The method for design of free-form surface proposed here can be widely applied in imaging systems and non-imaging systems.For example,it can be used in a microscope observing micro/nano materials.It leads to the simplification of the microscope and some special functions.For instance,instead of confocal lasing scanning,the microsope using a special free-form surface can achieve 3-dimentional images.