Deployment costs of large aperture systems in space or near-space are directly related to the weight of the system. In order to minimize the weight of conventional primary mirrors and simultaneously achieve an agile system that is capable of a wider field-of-view (FOV) and true optical zoom without macroscopic moving parts, we are proposing a revolutionary alternative to conventional zoom systems where moving lenses/mirrors and gimbals are replaced with lightweight carbon fiber reinforced polymer (CFRP) variable radius-of-curvature mirrors (VRMs) and MEMS deformable mirrors (DMs). CFRP and MEMS DMs can provide a variable effective focal length, generating the flexibility in system magnification that is normally accomplished with mechanical motion. By adjusting the actuation of the CFRP VRM and MEMS DM in concert, the focal lengths of these adjustable elements, and thus the magnification of the whole system, can be changed without macroscopic moving parts on a millisecond time scale. In addition, adding optical tilt and higher order aberration correction will allow us to image off-axis, providing additional flexibility.Sandia National Laboratories, the Naval Research Laboratory, Narrascape, Inc., and Composite Mirror Applications, Inc. are at the forefront of active optics research, leading the development of active systems for foveated imaging, active optical zoom, phase diversity, and actively enhanced multi-spectral imaging. Integrating active elements into an imaging system can simultaneously reduce the size and weight of the system, while increasing capability and flexibility. In this paper, we present recent progress in developing active optical (aka nonmechanical) zoom and MEMS based foveated imaging for active imaging with a focus on the operationally responsive space application.
We report a full design process-finite element modeling, fabrication, and characterization-of adaptive doublet polymer lenses. A first-order model was developed and used to design fluidic doublets, analogous to their glass counterparts. Two constant-volume fluidic chambers were enclosed by three flexible membranes, resulting in a variable focal length doublet with a clear aperture of 19.0 mm. Chromatic focal shift was then used to compare numerical modeling to experimentally measured results over a positive focal length range of 55-200 mm (f/2.89 to f/10.5).
Unique liquid crystal (LC) spatial light modulators (SLM) are being developed for foveated imaging systems that provide wide field-of-view (FOV) coverage (±60° in azimuth and elevation) without requiring gimbals or other mechanical scanners. Recently, a transmissive-SLM-based system operating in the visible (532 nm) has been demonstrated. The LC SLM development is addressing implementation issues through the development of high figure-of-merit (FoM) LC materials and transmissive high-resolution SLMs. Transmissive SLM operation allows the foveated imaging configuration to be very compact using a very simple lens system. The reduction in the size, weight and cost of the imaging optics and in data acquisition/processing hardware makes the foveated approach attractive for small platforms such as unmanned airborne vehicles (UAVs) or missile seekers.
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