A miniature imager is demonstrated using a metaform—a rotationally variant optic with an integrated metasurface.

A freeform pushbroom hyperspectral imager design was investigated as a combination of a freeform reflective triplet imager and a freeform reflective triplet spectrometer used in double-pass. The design operates at about F/2 with a 15-degree cross-track field-of-view and a 30 mm entrance pupil diameter. The design process led to achieving a small volume of less than 2 liters that fits comfortably within a 3U CubeSat geometry, exemplifying the compactness of this hyperspectral imager. We report the freeform sag departures and maximum slopes of the freeform surfaces, as well as the manufacturing tolerances together with an evaluation of the system stray light, all of which highlight the feasibility of a design in this class to be manufactured. This design uniquely positions itself on the landscape of compact hyperspectral imagers.

In rotationally symmetric lens design, there are rule-of-thumb boundaries on field-of-view and aperture for well-known design forms that provide valuable information to the designer prior to starting a design. In the design space of unobscured three-mirror imagers, freeform optics have been shown to provide a significant benefit over conventional surface shapes, but the degree to which they improve the performance for any given combination of field-of-view, entrance pupil diameter, and F-number remains unknown. Thus, designers of these systems are not afforded any pre-design information to inform their specification decisions. Here, we designed over 200 systems to establish a first-of-its-kind roadmap of specification ranges over which an unobscured three-mirror imager using freeform surfaces can achieve diffraction-limited performance in the visible spectrum. The scalability of the findings to the infrared regions of the spectrum is also addressed.

Refractive eyepiece design forms are often limited by chromatic aberrations and require a mix of glass types to achieve sufficient correction, thus they are not conducive to manufacture in volume. Reflective surfaces are inherently achromatic and can be produced in volume, but rotationally symmetric reflective surfaces are either used with lossy obscurations or are incapable of correcting rotationally variant aberrations when used in an unobscured form. Freeform optics enable unobscured reflective design forms with excellent image quality. Here, we document the design, fabrication, and assembly of an all-reflective high-end electronic viewfinder that shows the applicability of freeform surfaces to eyepiece design forms.

An approach to designing multiconfiguration afocal telescopes is developed and demonstrated. Freeform surfaces are used to maximize the achievable diffraction-limited zoom ratio while staying in a compact volume for a two-position multiconfiguration afocal optical system. The limitations of these systems with three-mirror beam paths are discussed and subsequently overcome by introducing an additional degree of freedom. In a four-mirror beam path system, the goal of a 5x zoom ratio is achieved with a compensated exit pupil and diffraction-limited performance. A significant benefit in optical performance when using freeform surfaces is shown compared to more conventional surface types.

Nodal Aberration Theory (NAT) was developed to explain the field dependency of aberration field centers in the image plane of nominally rotationally symmetric optical systems that have lost their symmetry through misalignments. A new insight into the theory led to calculating the sigma vectors, which locate the aberration field centers, using the angle between a real-ray trace of the optical axis ray (OAR) and the normal of the local surface where “local” refers to the object and image optical spaces of that surface. Here, we detail the sigma vector calculations for general optical systems and provide an experimental investigation of a misaligned system with a high-precision customized Cassegrain telescope. In the simulations, a Newtonian telescope, a Cassegrain telescope, and a three-mirror anastigmat telescope were misaligned intentionally in ray-tracing software. The sigma vectors were calculated analytically for the third-order aberrations of astigmatism and coma. Experimentally, the same perturbations were implemented for the Cassegrain telescope system, and the aberrations were quantified through interferometric measurements on a grid of field points in the image plane that verified the analytical derivation and simulations.