Design tools for freeform optics

Abstract

Freeform Optical surfaces are defined as any non-rotationally symmetric surface or a symmetric surface that is rotated about any axis that is not its axis of symmetry. These surfaces offer added degrees of freedom that can lead to lower wavefront error and smaller system size as compared to rotationally symmetric surfaces. Unfortunately, freeform optics are viewed by many designers as more difficult and expensive to manufacture than rotationally symmetric optical surfaces. For some freeform surfaces this is true, but a designer has little or no feedback to quantify the degree of difficulty for manufacturing a surface. This paper describes a joint effort by Optical Research Associates (ORA) and the Precision Engineering Center (PEC) at North Carolina State University to integrate metrics related to the cost and difficulty of manufacturing a surface into the merit function that is used during the design of an optical system using Code V®. By incorporating such information into the merit function, it is possible to balance optical performance and manufacturability early in the design process.

Metrology of freeform shaped parts

“…Designers prefer to select rotationally symmetric surface shapes for which the manufacturability issues are understood, rather than specify a design based on the properties of a freeform surface. For this reason, new optical design tools [51] have been developed to improve the manufacturability of these complex surfaces, in order to keep costs under control. Even with advanced design tools and ultra precision manufacturing technologies, the required accuracy of optical surfaces can often not be achieved in a deterministic manufacturing process.…”

“…The optical design includes four large, fast, off-axis, highly aspheric mirrors and one off-axis concave biconic mirror [15] [14] [52] [164]. The freeform mirror was introduced to help reduce the size of the system by an order of magnitude [51]. Significant reduction in size can dramatically reduce the use of exotic materials (such as beryllium) and the ensuing mass reduction provide enhanced performance for lightweight space systems.…”

Design of freeform optics

“…Figure 3 is a design example of two reflectors using this method. B 1 is the incoming beam, and B 2 is the output beam, which consists of parallel light rays propagating in the same dirction as B 1 . The rays in B 1 are reflected by igure 2 Sketch of the setting and irradiance distribution [13].…”

“…Freeform optics is defined as any nonrotationally symmetric surfaces or microarray surfaces [1]. There are three main ways to describe the freeform surfaces, i.e., NURBS [2], XY polynomial [3], and radial basis function representation [4][5][6][7][8].…”

Review of optical freeform surface representation technique and its application

“…Owing to their abundant degrees of freedom and strong ability of aberration correction, optical aspheric and freeform surfaces are strong candidates. From the geometrical viewpoint, 1 an optical freeform surface has nonrotationally symmetric features. From the aspect of fabrication and design, 2 an optical freeform surface is regarded as an optical surface that leverages a third independent axis during the fabrication process to form the optical surface with asdesigned nonsymmetric features.…”