No abstract

A multispectral camera records image data in various wavelengths across the electromagnetic spectrum to acquire additional information that a conventional camera fails to capture. With the advent of high-resolution image sensors and color filter technologies, multispectral imagers in the visible wavelengths have become popular with increasing commercial viability in the last decade. However, multispectral imaging in longwave infrared (LWIR, 8–14 μm) is still an emerging area due to the limited availability of optical materials, filter technologies, and high-resolution sensors. Images from LWIR multispectral cameras can capture emission spectra of objects to extract additional information that a human eye fails to capture and thus have important applications in precision agriculture, forestry, medicine, and object identification. In this work, we experimentally demonstrate an LWIR multispectral image sensor with three wavelength bands using optical elements made of an aluminum (Al)-based plasmonic filter array sandwiched in germanium (Ge). To realize the multispectral sensor, the filter arrays are then integrated into a three-dimensional (3D) printed wheel stacked on a low-resolution monochrome thermal sensor. Our prototype device is calibrated using a blackbody and its thermal output has been enhanced with computer vision methods. By applying a state-of-the-art deep learning method, we have also reconstructed multispectral images to a better spatial resolution. Scientifically, our work demonstrates a versatile spectral thermography technique for detecting target signatures in the LWIR range and other advanced spectral analyses.

Multispectral imaging involves capturing the same scene at different wavelengths using various narrowband filters stacked or integrated into digital camera sensors. This technology makes it possible to extract the additional information that a human eye or conventional camera fails to capture and thus has important applications in object identification, precision agriculture, and medicine. Multispectral imaging in visible wavelengths is readily possible due to the availability of digital imaging sensors and existing narrowband filter designs like metal-dielectric-metal films, dielectric films, or Fabry-Perot cavities [1-2].Multispectral imaging in thermal longwave infrared (LWIR) wavelengths of 8-14 µm range has more advanced applications as they can see through fire, detect various gases, and investigate materials non-destructively through thermal signatures. However, conventional thermal image sensors can image in a single spectral band only. Thermal multispectral imaging is hindered by traditional filter technology where many layers of different materials are required for obtaining various spectral bands and limited wavelength tunability. On-chip integration of the infrared filters on the thermal image sensors to build a compact multispectral thermal camera is still an emerging area [3-5].In the current work, we design and demonstrate a low-cost single sensor-based multispectral thermal sensor system composed of copper-based plasmonic imaging filter mosaic (multiple spectral filters are fabricated on a single substrate using only one lithography step and two deposition steps) integrated into an uncooled monochrome thermal sensor. The proposed work is mass-fabricable, scalable, and integrable, thereby leveraging next-generation LWIR thermal snapshot multi-and hyperspectral imaging.