Abstract: Light beam detection is taught in method and apparatus where a light source of coherent light is directed toward a reflecting hologram made to simulate a parabolic mirror to generate light beams detected by photoreceptors along one side of an opto-frame, such receptors being scanned in a manner to preclude false detection of an object within the field of light. An an alternative, multiple light sources are used with a single receptor and an appropriate hologram.

Abstract: A system and apparatus utilizes a source of coherent light located at the focal point of reflecting surfaces oriented to develop parallel beams of light extending over a given area with adjacent sides made to include arrays of light detectors scanned sequentially in a direction away from the source of light so as to detect the shadow cast by an object relative to the reflected light. Alternatively, a photodetector is positioned at the focal point of the reflectors to receive light emitted by individual ones of emitters. Reflecting surfaces are contemplated which simulate a parabolic shape.

Abstract: An input device which can be employed to input commands to a computer directly through a CRT display is disclosed. The input device employs a plurality of infrared light emitting diodes and phototransistors aligned in individual emitter-detector pairs. Infrared beams from the emitter cross the display field before striking the corresponding detector. Emitters and detectors are sequentially activated and each emitter is pulsed or modulated at a frequency different from the variation of ambient conditions during each emitter activation interval. The detection circuitry thus can distinguish the varying emitter signal from ambient or spurious variations. A number of pulses at the pulsed or modulated emitter frequency would be detected unless an opaque element were blocking the particular beam.