High Throughput Visible-Wavelength Multispectral Filter Arrays via Spectral Multiplexing

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Space Technology The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: To design and fabricate a multiplexing multispectral filter array covering the visible wavelengths that achieves a higher optical throughput than a narrowband array with equivalent bandwidth and spectral resolution. DESCRIPTION: Describe the work you would like to see accomplished to meet the objective stated above. Character limit 25,000. NOTE: Please do not write any Acronyms in the Topic Description. Spell out everything. Also no mathematical symbols. To design and fabricate a multiplexing multispectral filter array covering the visible wavelengths that achieves a higher optical throughput than a narrowband array with equivalent bandwidth and spectral resolution. Current visible-wavelength multispectral filter array technologies suffer from low light throughput because every pixel on the sensor only measures a single wavelength at a single spatial location. Multiple pixels are then considered together to construct the spectral signature over that group of pixels. This approach, while intuitive, leads to low light levels as the spectral resolution increases, since each pixel sees an ever-smaller piece of the object spectrum. The result of this is that high spectral resolution hyperspectral video becomes difficult due to the high integration times necessary to measure the signal. To resolve this issue, the performer will design and fabricate a visible-wavelength multiplexing multispectral filter array, where each filter is sensitive to many wavelengths at once. The performer will then mount their fabricated array onto an off-the-shelf monochromatic camera and demonstrate scene sampling and demosaicking. Success will be defined by the SNR, integration time, and spectral resolution and bandwidth compared to those of an off-the-shelf narrowband multispectral filter array. PHASE I: Modeling and simulation will be performed to determine a recipe for depositing a multiplexing filter array onto glass. The simulated filter transmission spectra will be used to model the sampling and demosaicking of a standard hyperspectral test image. Facilities for filter array fabrication will be identified by the performer. PHASE II: The multispectral filter array will be fabricated using the facilities identified by the performer during the Phase I. The performer will then characterize the array and align and mount it to a calibrated sensor. Hyperspectral measurements will then be acquired by the camera, demosaicked to recover the hyperspectral datacube, and then compared to imagery of the same scene acquired with an off-the-shelf pushbroom hyperspectral camera. The Phase II deliverable will be the fabricated filter array attached to the provided sensor. PHASE III DUAL USE APPLICATIONS: The spatial and spectral resolution of a camera with the affixed filter array will be characterized. A mounting system will be built for the camera to allow it to be attached to an off-the-shelf drone. A field test will be performed in which hyperspectral video of multiple moving ground targets with diverse spectral content will be acquired from a drone. REFERENCES: Harwitt, M. and Sloane, N., "Hadamard Transform Optics," Academic Press, 1979; Oliver, J. et al., Filters with random transmittance for improving resolution in filter-array-based spectrometers, Opt. Expr., 21(4), 2013; Bian et al., "A low-cost integrated hyperspectral imaging sensor with full temporal and spatial resolution at VIS-NIR wide range," arXiv, arXiv:2306.11583v1, 2023.; KEYWORDS: Multispectral Filter Array; Multiplexing Optics; Hyperspectral Imaging; Remote Sensing; Optical Filter Fabrication; Optical Coatings