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Conformal Beam Steering for High Resolution Ladar

Description:

TECHNOLOGY AREA(S): Sensors 

OBJECTIVE: Develop conformal optical steering system for a LADAR sensor suitable for scaling via tiling small sub-apertures to realize larger, meter class apertures with low size, weight, and power. This device should be amenable for steering the field of view (FOV) of a high-resolution LADAR imaging receiver. 

DESCRIPTION: The Air Force has pressing requirements for operating in contested environments where intelligence, surveillance, and reconnaissance (ISR) assets cannot operate freely. The Air Force requires high confidence ID for high value targets to protect air crews and to establish air superiority. Two approaches considered are deployment of large aperture sensors, such as LADAR, to provide stand-off imaging capability, and use of attritable, unmanned aerial systems (UAS) for penetrating ISR and strike. Both approaches need enhanced target ID capabilities of LADAR as well as persistent passive imaging via mid-wave or long-wave imaging for cueing and situational awareness. Conventional optical systems rely on gimbaled optics, which significantly limit the aperture size and increase Cost, Size, Weight and Power (C-SWAP). For large apertures, the pod cannot physically accommodate the gimbal size required and a conformal approach is the only way forward. The attritable platform has tight C-SWAP restrictions, which imposes severe performance trades for gimbaled approaches. Non-mechanical beam steering (NMBS) is a technology that provides the ability to direct a laser beam without physical movement of the optical elements. NMBS offers performance advantages over mechanical systems with reduced weight, random access to steering directions, expanded field of view (FOV), and higher steering speeds. In addition NMBS offers logistical advantages, with electronic optical calibration, high precision and accuracy, and sealed long life components. NMBS devices have been developed that steer to discrete points at high efficiency using a stack of polarization gratings, or addressable points with a single optical phased array (OPA). The goal of this effort is to demonstrate a conformal optical steering system that steers 2 micron light. The steering system should use smaller sub-apertures with a well-defined optical phase relation between them to create larger effective apertures. This technique is meant to create an essentially scalable fabrication method for realizing arbitrarily larger effective apertures up to at least 6 inches diameter with a goal of up to 12 inches diameter. For example, the use of nanophotonic optical elements, or metasurfaces, for creating engineered optical properties of light has been shown to be a versatile technique for beam shaping, but methods for scaling this to larger apertures remains a challenge. This and other approaches for beam steering or shaping will be considered, with an emphasis on techniques which can be readily scaled to larger sizes through repeated patterning of smaller sub-apertures. The final steering system should be capable of steering to >(+/-)15 degrees in one dimension, (goal (+/-)30 degrees), with >80% power in steered beam. Devices should operate at >200Hz, with a goal of 1 kHz operation. Commercial application of a conformal low C-SWAP optical steering would have similar benefits for civil uses of LADAR mapping. Government materials, equipment, data or facilities are not necessary. 

PHASE I: In this initial phase, device concepts will be developed, evaluated, and computer modeled. Design challenges and trade-offs will be tabulated and areas in need of additional R&D will be identified. Critical factors to consider are, maximum theoretical transmission, aperture size, low SWAP packaging, and demonstrating that the technology can achieve requirements through models. SWaP guidelines to consider include the potential for aperture sizes from 6 inches up to about 40 inches in diameter, weight under 5 kilograms, and average power usage under 10 W. Preliminary designs should be developed for Phase II. 

PHASE II: Devices will be constructed and tested for beam steering efficiency, aperture, and SWAP requirements. Tests will be conducted to verify performance parameters of the device with a short-wave infrared camera surrogate for a LADAR. Iteration on designs and improvements will be made as the production process is refined and preliminary designs for a Phase III device should be made. 

PHASE III: A flight ready version of the design will be built, steering efficiencies, and size, weight and power of both device and control system in form factor for integration in a UAS. Current manufacturing process will be evaluated and refined to improve yield while reducing cost. 

REFERENCES: 

1. Optical Phased Array Technology, Paul F. McManamon et. al., Proceedings of the IEEE, Vol. 84, No. 2, February 1996.; 2. High-Efficiency All-Dielectric Metasurfaces for Ultracompact Beam Manipulation in Transmission Mode, Mikhail I. Shalaev et. al., Nano Letters, 15 (9), pp 6261–6266 (2015); 3. Large area metalenses: design, characterization, and mass manufacturing, Alan She et. al., Optics Express Vol. 26, No. 2 pp. 1573-1585, (2018); 4. Wide-Angle, Nonmechanical Beam Steering Using Thin Liquid Crystal Polarization Gratings, Jihwan Kim et. al., Advanced Wavefront Control: Methods, Devices, and Applications VI, Proc. of SPIE, Vol. 7093, 709302, (2008).

KEYWORDS: NMBS, LIDAR, LADAR, Non-mechanical, Steering, Beam Steering, Optical, Conformal, Sub-aperture, Metasurfaces 

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