Freeform optics for imaging

TLDR

Freeform optics has enabled compact, high‑performance imaging systems and offers opportunities across applications from extreme ultraviolet lithography to space optics. This review traces the history of freeform optics in imaging, defines the technology, discusses concurrent engineering and aberration theory, and outlines future directions. The authors describe freeform optics design, concurrent engineering, aberration theory, deterministic CNC grinding, polishing, diamond machining, and address mid‑spatial frequency errors inherent to fabrication. The review identifies that freeform optics metrology is sparse yet diverse, and highlights demonstrated measurement techniques.

Abstract

In the last 10 years, freeform optics has enabled compact and high-performance imaging systems. This article begins with a brief history of freeform optics, focusing on imaging systems, including marketplace emergence. The development of this technology is motivated by the clear opportunity to enable science across a wide range of applications, spanning from extreme ultraviolet lithography to space optics. Next, we define freeform optics and discuss concurrent engineering that brings together design, fabrication, testing, and assembly into one process. We then lay out the foundations of the aberration theory for freeform optics and emerging design methodologies. We describe fabrication methods, emphasizing deterministic computer numerical control grinding, polishing, and diamond machining. Next, we consider mid-spatial frequency errors that inherently result from freeform fabrication techniques. We realize that metrologies of freeform optics are simultaneously sparse in their existence but diverse in their potential. Thus, we focus on metrology techniques demonstrated for the measurement of freeform optics. We conclude this review with an outlook on the future of freeform optics.