Document Type

Conference Proceeding

Publication Title

Proceedings of SPIE - the International Society for Optical Engineering


A real-time diffraction based optical processed 3-D shape recognition system has been built and demonstrated. The system uses an Ar-ion laser interferometer to project variable spatial frequency structural illumination on 3 dimensional targets which are viewed by a camera. The video data is mixed with a computer generated mask (converted to RS-170 video) and the resulting output video signal is sent to a liquid crystal television (modified to function as a spatial light modulator) which is illuminated by a He-Ne laser. The video mixing process, based on a commercial Chroma-Key circuit, generates an arbitrary moire pattern which is a function of the 3 dimensional shape of the target (indicated by the distorted structured illumination) and of the computer generated mask. As an example, the output pattern could be a 1 dimensional Fresnel zone plate (FZP) when the shape of the object is recognized. In this case, the laser illuminated zone plate produces a bright line focus at the predicted focal distance for the correct target, a reduced intensity line focus for a damaged target, and no output for a totally different target. The result is a mixed video-optical processing system that could be used for real-time quality level sorting or other automated inspection requirements. Other types of diffractive masks are simulated with the goal of increasing the area of target inspection and recognizing and discriminating between different targets with a single mask. Limitations and improvements in the current system are discussed.

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