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Designing with freeform optics makes it possible to correct imaging systems to high-performance levels in a compact format. To justify the extra challenges inherent in the design, fabrication, metrology, and assembly of systems utilizing freeform optics, engineers need a realistic understanding of the performance that can be expected. The real-world performance of these systems has remained under-explored in the literature, a factor that may dissuade the adoption of freeform optics. In this work, the MTF of an F/3, 3° diagonal full FOV, 250-mm aperture freeform telescope is characterized at multiple field angles using an off-axis parabolic collimator. The freeform optic components required minimal alignment steps and no post-polishing. Twenty-seven sub-aperture tilted knife-edge tests were conducted to evaluate the correlation between form error and image quality. The telescope’s image quality was determined to be consistent with the design specification, which was 30% MTF at 76 lp/mm (70% of the sensor-array Nyquist frequency) across the entire field.
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Freeform optics: introduction
This feature issue of Optics Express highlights 28 state-of-the-art articles that capture a snapshot of the recent developments in the field of freeform optics. As an introduction, the editors provide an overview of all published articles, which cover a broad range of topics in freeform optics. The wide variety of applications presented here demonstrates that freeform optics is a growing and vibrant field with many more innovations to come.
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- PAR ID:
- 10429831
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 30
- Issue:
- 4
- ISSN:
- 1094-4087
- Page Range / eLocation ID:
- 6450
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Freeform Fresnel optics represent an emerging category of modern optics that reproduces powerful optical functionalities while maintaining an ultra-compact volume. The existing ultra-precision machining (UPM) technique faces technical challenges in meeting the fabrication requirements for freeform Fresnel optics because of the absence of appropriate geometry definition and corresponding tool path planning strategy to overcome the extreme asymmetry and discontinuity. This study proposes a new scheme for ultra-precision machining using four axes (X,Y,Z,C) to fabricate freeform Fresnel optics, including a general geometry description for freeform Fresnel optics, the quasi-spiral tool path generation strategy to overcome the lack of rotary symmetry, and the adaptive tool pose manipulation method for avoiding tool interference. In addition, the tool edge compensation and the adaptive timestep determination are also introduced to enhance the performance and efficiency of the proposed scheme. The machining of two exemplary freeform Fresnel lenses is successfully demonstrated. Overall, this study introduces a comprehensive routine for the fabrication of freeform Fresnel optics and proposes the adaptive tool pose manipulation scheme, which has the potential for broader applications in the ultra-precision machining of complex or discontinuous surfaces.more » « less
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Freeform optics are transforming the way optical systems are designed. Unlike traditional lenses and mirrors, which are typically limited to simple, symmetrical shapes, freeform optics allow for total freedom of the surface shape. This flexibility has led to smaller, lighter, and more capable optical devices, improving performance factors such as the field of view and numerical aperture. However, this design freedom also introduces new layers of complexity. In this review, we examine recent methods developed to address these challenges. We group these approaches into four categories: those based on aberration theory, direct design techniques, automated optimization methods, and design-for-manufacture methods. We conclude by looking ahead to the future of freeform optics in system design.more » « less
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Reimaging telescopes have an accessible exit pupil that facilitates stray light mitigation and matching to auxiliary optical systems. Freeform surfaces present the opportunity for unobscured reflective systems to be folded into geometries that are otherwise impracticable with conventional surface types. It is critical, however, to understand the limitations of the enabled folding geometries and choose the one that best balances the optical performance and mechanical requirements. Here, we used the aberration theory of freeform surfaces to determine the aberration correction potential for using freeform surfaces in reimaging three-mirror telescopes and established a hierarchy for the different folding geometries without using optimization. We found that when using freeform optics, the ideal folding geometry had 9× better wavefront performance compared to the next best geometry. Within that ideal geometry, the system using freeform optics had 39% better wavefront performance compared to a system using off-axis asphere surfaces, thus quantifying one of the advantages of freeform optics in this design space.more » « less
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When using freeform surfaces in optical design, the field dependence of the aberrations can become quite complex, and understanding these aberrations facilitates the design process. Here we calculate the field dependence of low-order Zernike astigmatism (Z5/6) up to the eighth order in nodal aberration theory (NAT). Expansion of NAT astigmatism terms to the eighth order facilitates a more accurate fit to the Zernike astigmatism data. We then show how this estimated field dependence can be used to quantitatively analyze a freeform telescope design. This analysis tool adds to the optical designer’s arsenal when up against the challenge of designing with freeform optics. ©2019 Optical Society of America https://doi.org/10.1364/JOSAA.36.002115more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1364/OE.454788
