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Innovative Optics for Wide Field of View Infrared Sensors


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics OBJECTIVE: Develop innovative and affordable wide aperture optics technology for imaging sensors operating in the mid-wave infrared (MWIR) and short-wave infrared (SWIR) bands. DESCRIPTION: Electro-optic and infrared (EO/IR) video imaging sensors (cameras) are widely used for situational awareness, surveillance, and targeting. The Navy is deploying such cameras in multiple spectral bands, covering both wide and narrow fields of view (FOV). Wide field of view (WFOV) cameras are particularly expensive as they employ large focal plane array (FPA) sensors and, to gather sufficient light, these cameras must have large aperture optics (lenses). In the infrared (IR), these lenses are especially costly, not benefitting from large commercial economies of scale as exists for camera lenses in the visible spectrum. Furthermore, because of the shallow depth of field inherent in such large aperture lenses, the optical elements (and the FPA) must be aligned to extremely tight tolerances in order to maintain the high resolution required. Tolerances for axial alignment on the single-micron level are not uncommon. In addition, the optical assembly must be rugged enough for shipboard deployment, maintaining its alignment in spite of operational shock, vibration, and extremes of temperature. Consequently, not only are the optical elements (lens elements) expensive, but the optical housing (lens barrel) is expensive as well. Finally, the precision assembly processes required to achieve such tight optical alignment are labor intensive and the labor is highly skilled in nature. The result is that such cameras are excessively costly. The Navy needs an innovative technology for focusing IR light onto FPA sensors with high optical resolution. The goal is to dramatically reduce cost without compromising performance. A nominal cost reduction of 5:1 is desired for the optical assembly (based on the current state-of-the-art for conventional optics), which, for this purpose, does not include the material cost of the FPA but does include the optical elements, the optical assembly, and alignment of the optics with the FPA. A solution applicable to both the MWIR and the SWIR is desired. However, the technology may be demonstrated in either band, at the discretion of the proposer. A maximum effective aperture of f1.0 is desired with a 90° FOV and coverage sufficient for a 2k X 2k pixel FPA with 10 µm pitch. The light fall-off from FPA center to the corner of the FPA shall not exceed a factor of 2.0. The depth of field shall be sufficient to resolve single pixel targets. Note that all requirements apply at full aperture. Optical aberrations are acceptable provided they can be compensated for in post processing and provided that they are not so severe as to inhibit resolution of a single pixel target lying anywhere in the imaged field. In demonstrating a solution, and in order to reduce cost, a large format FPA meeting the dimensions given above need not be included in the prototype. A smaller FPA (or multiple FPAs) may be used provided it can be shown that the required image quality defined above is achieved over the extent of the large format FPA. This effort anticipates a hardware solution for a single large format FPA that yields high image quality (resolution, dynamic range, noise, etc.) video capture in real time. Image capture shall accommodate a video frame rate of 30 frames per second. Solutions that attempt to re-construct images or combine images from multiple FPAs are undesirable. Predominantly software-based solutions – that is solutions based on extensive post processing of the captured image data will not be considered. Solutions incorporating electro-mechanical compensation of optical elements are permitted providing the compensation mechanism does not reduce the integration time available to the FPA. Any electro-mechanical components included in the solution must also be shown to have a (maintenance-free) life expectancy comparable to the FPA. At the end of the effort the prototype shall be delivered to Naval Surface Warfare Center (NSWC) Crane Division. Included in the prototype will be the FPA (or FPAs) used to demonstrate the image quality obtained by the solution, and any controllers, power supplies, housings, coolers, output interfaces, special processing hardware, custom software, fixtures, and specialized tools necessary to replicate testing of the prototype. A cost estimate for production and integration of the solution will be performed to assess the reduction in cost associated with the technology. The cost assessment shall be benchmarked to the cost of a conventional optical design. PHASE I: Develop a concept for a large aperture optical system that meets the objectives stated in the Description. Demonstrate the feasibility of the concept in meeting the Navy’s need. Analyze the effect on image quality and predict the benefits for cost reduction. Feasibility shall be demonstrated by a combination of analysis, modeling, and simulation. The Phase I Option, if exercised, will include an initial sensor specification, test specification, and capabilities description necessary to build and evaluate prototype hardware in Phase II. PHASE II: Develop and demonstrate a prototype large aperture optical system for imaging IR sensors based on the concept, analysis, preliminary design, and specifications resulting from Phase I. Demonstration of the large aperture optics technology shall be accomplished through test of a prototype in a laboratory or sheltered outdoor environment. At the conclusion of Phase II, prototype hardware shall be delivered to NSWC Crane along with complete test data, installation and operation instructions, and any auxiliary software and special hardware necessary to operate the prototype. PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Government use. Develop specific optical designs for Navy sensor systems. Establish hardware configuration baselines, produce support documentation, production processes, and assist the Government in the integration of the optical technology into existing and future WFOV imaging sensor systems. The technology resulting from this effort is anticipated to have broad military application. In addition, there are law enforcement and security applications. Scientific applications include satellite and aerial imagery. REFERENCES: 1. Driggers, Ronald G., et al. Introduction to Infrared and Electro-Optical Systems, Second Edition. Boston: Artech House, 2012. 2. Gibson, Daniel, et al. "Diffusion-based gradient index optics for infrared imaging.” Optical Engineering 59 (2020): 112604-1-22. KEYWORDS: Video Imaging; Imaging Sensors; Wide Field of View Cameras; FOV; Large Aperture Optics; Depth of Field; Optical Resolution
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