Applications of point-by-point design method in freeform imaging systems

摘要

Freeform surface can offer many degrees of design freedom for imaging system design, and can correct the aberrations in non-symmetric systems while decreasing the system size, mass, and number of elements. The point-by-point design methods overcome some drawbacks of traditional design methods for freeform imaging systems. Here we present the basic theory and applications of the point-by-point design method based on the construction-iteration process. This method considers the rays from multiple fields and different pupil coordinates simultaneously. The freeform surfaces can be calculated point-by-point based on the given object-image relationships or mapping relationship starting from an initial system consisting of decentered and tilted planes without optical power. The design results of this method can be taken as good starting points for further optimization. This method is first successfully employed in the design of off-axis freeform imaging systems. Then, with specific design strategies for different kinds of systems, this method is extended to the design of freeform systems with special configurations or special functions, including freeform imaging and afocal systems with a real exit pupil, freeform image-side telecentric systems, freeform imaging systems with dual field-of-views and dual focal-lengths, and freeform f-θ single lenses. Considering the refraction and reflection as well as the diffraction of grating for the rays coming from multiple wavelengths, multiple fields and different pupil coordinates, freeform imaging spectrometers can be also successfully designed. Finally, we extend the point-by-point design process to the automated design of high-performance freeform imaging systems. Compared with traditional design methods, this point-by-point design process significantly reduces the human effort and does not rely on advanced design skills and experience. In addition, the dependence on existing starting points is significantly reduced.