Seeing the Invisible: From Polarization-Sensitive Visual Systems in Nature to Bio-Inspired Sensing and Imaging Science and Technology
Prof. Nader Engheta
University of Pennsylvania
Certain animal species in nature have visual systems that are sensitive to light's polarization - a capability that is lacking in the
human eyes. Our eyes cannot effectively sense and utilize the polarization information without appropriate external instruments. However, the species with polarization
vision can detect this characteristic of image-forming light and can extract its information. Polarization is obviously an important feature of optical signals, and it
can be affected by surface shapes, materials, local curvature and features, and relative location of sources and objects, and thus it can provide useful information
about the observed scene and objects. What can one learn from this interesting ability of polarization sensing and detection in nature that has been evolved in certain
biological visual systems? Of course, two general types of questions may be asked about this ability. (1) How do these species detect and sense the light's
polarization?, (2) How do they use this ability? The first general question points to the biophysical mechanisms of polarization detection in such visual systems - a
topic that for sometime has been a subject of interest for biologists, zoologists, and recently neuroscientists, physicists, and engineers. The second question aims at
the functionality and advantages of this sensing mechanism in nature. In addition to the navigational utility of polarization sensing, it has been understood that some
species use polarization vision to enhance their ability to detect and classify targets, to see otherwise "transparent" targets, to the break the camouflage, and to
recognize conspecifics, etc.
Understanding the biophysical mechanism behind the polarization vision and reverse engineering its functionality and utility leads to exciting novel methods and
techniques in sensing and imaging with various applications. Motivated and inspired by the features of polarization-sensitive visual systems in nature, in my group we
have been developing various man-made, non-invasive imaging methodologies, sensing schemes and visualization and display schemes that have shown exciting and promising
outcomes with useful applications in system design. These techniques provide better target detection, enhanced visibility in otherwise low-contrast conditions, longer
detection range in optically scattering media, polarization-sensitive adaptation based on changing environments, surface deformation-variation detection (e.g., detection
of finger prints on a smooth surface using polarization-based vision), "seeing" objects in shadows, and other novel outcomes and applications.
In this talk, I will discuss several optical aspects of the biophysical mechanisms of polarization vision, and present sample results of our bio-inspired imaging
methodologies. In addition, I will briefly mention some of the other research activities in my group.