An afocal telescope system with adjustable magnification and field of view (FOV) modes for object searching and object inspection
Institute Reference: 2-24029
As applications for earth-viewing satellites become more diverse, the required specifications of on-board optical systems become increasingly complex and challenging to achieve with single fixed-focus imaging systems. All-reflective afocal optics provide a powerful tool for meeting complex and challenging optical system specifications because they are intrinsically achromatic, permit large aperture sizes, and can maximize the light throughput for a given aperture size. While high-performance optical systems using all-reflective afocal optics have been achieved in single-configuration systems, it has been challenging to achieve high-performance in multi-configuration all-reflective afocal optical systems.
Using freeform surfaces, we have developed a novel multiconfiguration afocal reflective system capable of switching between a low magnification wide FOV mode and a high magnification narrow FOV mode. This is achieved through systems with three-mirror or four-mirror beam paths, employing freeform optics to enable compact footprints while maintaining diffraction-limited wavefront performance.
For the three-mirror designs, the primary mirror can rotate to direct light to separate secondary mirrors, after which the light interacts with a shared tertiary mirror that can translate and rotate when switching configurations. A variation splits the tertiary into two separate mirrors, enabling up to a 4x zoom ratio.
For the four-mirror approach, a shared rotating primary mirror, separated secondary, and shared translating and rotating tertiary/quaternary mirrors are utilized. A variation separates the tertiary mirror into two parts for improved exit pupil quality at 4x/5x zoom while maintaining compactness. The use of higher-order freeform terms on the shared mirrors maximizes performance and minimizes aberrations.
The designs were optimized to achieve zoom ratios between 2x and 5x while satisfying constraints on wavefront error, exit pupil quality, and overall system volume.
Freeform optics offer significant improvements over conventional off-axis conic surfaces. For a 2x zoom ratio four-mirror system in a 50L volume, the freeform design achieved 12x better RMS wavefront error (0.026λ vs 0.27λ in the high-magnification mode) and ~2x better exit pupil quality. At 100L, freeform still provided 4.5x better wavefront (0.012λ vs 0.049λ) and 2x better pupil quality.
This technology is primarily applicable to satellite remote sensing/observation. The low-magnification mode provides wide‑field scene observation and high-magnification enables targeted high-resolution inspection activities. The afocal telescope system’s compact design makes it suitable for space-based applications with stringent size/weight constraints.
The university seeks to license this technology exclusively.