| abstract |
An optical identification element (8) includes an optical substrate (10) having at least one diffraction grating (12) disposed therein. The grating (12) having a plurality of colocated pitches Λ which represent a unique identification digital code that is detected when illuminated by incident light (24). The incident light (24) may be directed transversely from the side of the substrate (10) with a narrow band (single wavelength) or multiple wavelength source, in which case the code is represented by a spatial distribution of light or a wavelength spectrum, respectively. The element (8) can provide a large number of unique codes, e.g., greater than 67 million codes, and can withstand harsh environments. The element (8) can be used in any application that requires sorting, tagging, tracking or identification, and can be made on a micron scale 'microbeads' if desired, or larger 'macrobeads' for larger applications. The code may be digital binary or may be other numerical bases. |