Physics and Reverse-Engineering of Polarization Vision in Nature, Biologically-Inspired Polarization Imaging and Sensing
Dual tier micro-polarization array
In order to equip individual photo receptors in the image sensor with polarization sensitivity, a set of micropolarizer arrays have been designed. An array of micro-polarizers is created from a commercially available thin film known as Polyvinyl Alcohol (PVA). The final micro-polarization array contains two patterned thin film polarizers offset by 45 degrees with pixel pitch of 8 microns. The patterning and etching of the thin film polymer was achieved via an advance microfabrication procedure optimized for the polymer thin film. The measured extinction ratios on the micro polarization filters are ~1000 in the blue and green visible spectrum and ~100 in the red spectrum. The patterned single layer of PVA is presented in the figure below. Anisotropic etching with 1 micron under cutting of a 10 micron thick film has been achieved via selective reactive ion etching. The optical characteristics of the dual-axial micropolarizers offset by 45 degrees are presented in the figure bellow. The images (a), (b), (c) and (d) are recorded with 0, 45, 90 and 135 degrees of polarized light, respectively. In the image (a) (image (c)), the sample was illuminated with polarized light with polarization parallel (perpendicular) to the transmission axis of the PVA structures in the first tier i.e. with 0 (90) degree polarized light. Hence, the square structures in the first tier appear opaque in intensity in image (a) and transparent in image (c). Since the second tier is offset by 45 degrees, it is difficult to visualize its relative offset. The polarization properties of the second tier are clearly evident in image (b) and image (d). In image (b) (image (d)), the sample was illuminated with polarized light parallel (perpendicular) to the transmission axis of the PVA structures in the second tier i.e. with 45 (135) degree polarized light. Hence, the square structures in the second tier appear opaque in intensity in image (b) and transparent in image (d).
We are in the process of integrating micropolarizer arrays over the CMOS detector arrays. Various applications are being considered for these integrated bio-inspired imaging systems.
(a) (b) (c) (d)
For details regarding this image, please see, Viktor Gruev, Alessandro Ortu, Nathan Lazarus, Jan Van der Spiegel, and Nader Engheta, "Fabrication of a dual-tier thin film micropolarization array," Optics Express, Vol. 15, No. 8, pp. 4994-5007, April 2007.