Pattern recognition based on analysis of the summary ellipse polarization state in the Fraunhofer diffraction area

Abstract

A new method of pattern recognition is presented which is based on obtaining photoanisotropic copies on the dynamic polarization sensitive material. The amplitude image of the object is illuminated by a linearly polarized light with a wavelength actinic for this material. In result a photoanisotropic copy of this image is induced on the polarizationsensitive material. In recognition process, a photoanisotropic copy is illuminated by circularly polarized light of a nonactinic wavelength. The distribution of elliptical polarization occurs behind a photoanisotropic copy and reduces to a summary ellipse in the Fraunhofer diffraction region. The parameters of this ellipse are related to the characteristics of the original object and uniquely identify the initial object. The polarization-holographic diffraction element developed by us enables to determine summary ellipse parameters - to obtain all the Stokes parameters in real time and to compare obtained results with recognizable object etalon in database. The method invariance to position, scale and rotation of pattern are investigated. The resolution and sensitivity of this method were also determined. The dynamic polarizationsensitive materials are reversible, with practically unlimited number of recording-deleting cycles. To obtain a photoanisotropic copy of another object on the same material, the previous copy should be deleted with a pulse of circularly polarized actinic light, then a next copy can be recorded. A laboratory model of the recognition device, appropriate software and a theoretical model were created. Database have been obtained by using images of various objects.