The ultrasensitive eyes of mantis shrimp are the inspiration behind a new kind of optical sensor that is small enough to fit on a smartphone, yet capable of performing hyperspectral and polarimetric imaging. A prototype of the sensor, called the stomatopod-inspired multispectral and polarization sensitive (SIMPOL) sensor, was able to simultaneously register four spectral channels and three polarization channels.
By comparison, a CCD sensor may have only three spectral imaging sensors that detect red, green, and blue, and only two polarization channels.
Additionally, the SIMPOL prototype was able to measure the four color channels at one point, whereas CCD sensors rely on imaging sensors spread across several points.
Spectral imaging of a scene containing objects with different colors, as well as the letters NCSU, which contain different polarization states. Courtesy of Ali Altaqui.
Many AI programs can make use of data-rich hyperspectral and polarimetric images, said Michael Kudenov, an associate professor of electrical and computer engineering at North Carolina State University and co-corresponding author on a paper describing the work. Current equipment necessary for capturing those images, however, is somewhat bulky, he said, adding, “Our work here makes smaller, more user-friendly devices possible. And that would allow us to better bring those AI capabilities to bear in fields from astronomy to biomedicine.”
The sensor’s design pulls from the structural and functional features of the mantis shrimp’s eye, which allow it to capture subtle gradations of color. Its compound eye contains spectrally selective elements, called pigmented retinular cells, and polarization-sensitive elements, their tiered microvilli in the rhabdom — a structure beneath the cornea in the compound eyes of arthropods. These elements are stacked vertically along a single optical axis called an ommatidium. As light propagates deeper into the stack, the shrimp can increase the volume of spectral and polarization information it can abstract.
“Analogously, our organic sensor comprises spectrally selective elements (the folded retarders) and polarization-sensitive elements (the organic photovoltaics) that are vertically stacked along a single optical axis,” Ali Altaqui, a postdoctoral researcher at North Carolina State University, told Photonics Media. “The spectral and polarization information is detected in a similar manner as the mantis shrimp’s eye, enabling simultaneous spectral and polarimetric detection.”
The rhabdom contains tiered microvilli that are oriented in four unique directions, offset by 45°, across the mantis shrimp’s eye. That feature enables them to perceive polarized light.
“Comparatively, the organic photovoltaic cells comprise conjugated molecular chains that are aligned along a specific direction,” Altaqui said. “This feature allows our sensor to be polarization sensitive.”
With all that information, the sensor detected distinct chemical and geometric features. The ability to detect geometric features opens up the possibility of 3D imaging, which has been demonstrated to be possible using polarization imaging in conjunction with an algorithm related to the degree of polarization of light.
Though only a proof of concept, the researchers used modeling simulations to determine that the design could be used to create detectors capable of sensing up to 15 spatially registered spectral channels. According to Kudenov, SIMPOL’s color channels can discern spectral features 10× narrower than typical imaging sensors.
“Our work demonstrates that it is possible to create small, efficient sensors that can simultaneously capture hyperspectral and polarimetric images,” said Brendan O’Connor, co-corresponding author on the study and an associate professor of mechanical and aerospace engineering at North Carolina State University. “I think this opens the door to a new breed of organic electronic sensing technologies.”
The research was published in Science Advances (www.doi.org/10.1126/sciadv.abe3196).