Optical identification element having a non-waveguide substrate

摘要

An optical identification element including a non-waveguide optical substrate. The optical substrate has a volume and includes an inner region surrounded by an outer region. The inner region has an index of refraction that prevents the optical substrate from forming an optical waveguide. The optical substrate includes a diffraction grating within the volume, and the grating provides an output signal indicative of a code when illuminated by an incident light.