Optical touch screen systems using total internal reflection

A touch screen for a computing device, comprising:

• a housing;
• a layer of light-transmissive material mounted in said housing, comprising upper and lower surfaces, wherein said upper surface is exposed for touch by one or more objects from outside of said housing;
• a plurality of light emitters mounted in said housing underneath said upper surface, for emitting light beams;
• a first lens assembly mounted in said housing for directing the light beams emitted by said light emitters into said layer at an angle such that the light beams, when entering said layer, remain confined to said layer by total internal reflection at said upper and lower surfaces of said layer;
• a plurality of light detectors mounted in said housing underneath said upper surface, for detecting light beams and for generating outputs indicating the amounts of light detected;
• a second lens assembly mounted in said housing for directing light beams at a surface of said layer towards one or more of said light detectors;
• and
• a calculating unit, mounted in said housing and connected to said light receivers, for determining respective one or more locations of the one or more objects touching said upper surface, based on outputs of said light detectors,
• wherein light beams in said layer are scattered back into said layer at said upper surface when they come into contact with any of the objects, so that said second lens assembly directs them to more of said light detectors than had they not been scattered.