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Elliptical polarizers, tags and identification systems using frequency selective surfaces

Image Number 8 for United States Patent #7629569.

An optical combination includes a substrate, a linear polarizer on the substrate, and a first frequency selective surface (FSS) based elliptical polarization filter on the linear polarizer. The first FSS comprises at least one periodic pattern of spaced apart electrically conductive lines having a sub-wavelength line-to-line spacing orientated along a first axis. The pattern is operable to impose a phase differential for one orthogonal linear polarization state relative to the other linear polarization state for electromagnetic radiation having a wavelength between 400 nm and 1 mm, such as 1 .mu.m to 12 .mu.m. An identification system and associated method for identifying objects includes at least one tag having encoded information attached to the surface of an object to be identified, wherein the tag includes a first FSS-based elliptical polarization filter which provides the encoding. A remotely located receiver including a second FSS-based elliptical polarization filter and a linear polarizer optically coupled to the second filter is operable for differentially attenuating the first and second orthogonal polarization states allowing a determination whether the intensity pattern corresponds to the encoded information.

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