Construction method through forward and reverse ray tracing for a design of ultra-wide linear field-of-view off-axis freeform imaging systems

摘要

In this paper, a construction method through forward and reverse ray tracing for a design of ultra-wide linear field-of-view (FOV) off-axis freeform systems is proposed. The freeform initial system is numerically constructed by a point-by-point calculation. This method begins with a spherical system solved by the paraxial optical theory. In this method, the primary mirror is calculated through the reverse ray tracing; hence, the size and position of the aperture stop is not affected by the changes of mirrors. The fields in the reverse system are selected to cause certain beam overlaps on the primary mirror between adjacent fields. These overlaps offer a more uniform distribution of data points, improving the calculation of this mirror. As an example, an off-axis freeform system with an ultra-wide linear field-of-view of 70 degrees is designed by this method. The effective focal length of the system is 75 mm, and the F-number is 5.8. The diffraction-limited performance of this freeform system in the visible band and the near infrared and near ultraviolet bands validate the construction method presented in this paper.