Shadow detection in optical touch sensor through the linear combination of optical beams and grey-scale determination of detected shadow edges

Abstract

An optical based input touch display device with high resolution shadow detection using the linear splitting of waveguides among transmit and receive lenses and grey-scale calculations for shadow edge and center detection is disclosed. The apparatus includes a light source and a transmit waveguide optically coupled to the light source. The transmit waveguide includes a plurality of transmit waveguide grooves coupled to a plurality of groups of shared transmit lenses respectively. The plurality of groups of transit lenses, which are configured to generate a plurality of collimated light beams from the light source. A receive waveguide is also provided having a plurality of receive waveguide grooves coupled to a plurality of groups of shared receive lenses. The plurality of groups of receive lenses are configured to receive the plurality of collimated light beams. A photodiode array including a plurality of photodiodes are optically coupled to the plurality of receive waveguide grooves respectively. Each of the photodiodes is configured to receive light from the plurality of light beams received by the plurality of groups of receive lenses respectively. A processor is configured to detect shadow edge and/or shadow center of an interrupt in the plurality of collimated light beams.