PURPOSE: To reduce the number of photodetectors by stacking plural stages of light transmitters each constituted by forming a conic reflection surface which reflects a sidewise incident light in a specific direction and also arranging a photodetector which photodetects the light beam reflected by the reflection surface.
CONSTITUTION: The light transmitter 10 is constituted by forming the inverse conic hole 11 in the center of a disk made of transparent resin and forming the reflecting surface 12 by vapor-depositing metal such as chromium and aluminum on the circumferential surface of the hole, and then arranging the discoid photodetector 13 of nearly the same size with the large diameter part of the reflection surface 12 at the reverse center part. Those light transmitters are stacked in plural stages. When the light beam such as a laser beam is incident from the obligue direction, it is directed downward by the reflection surface 12 to enter the photodetector 13, which outputs an electric signal corresponding to the quantity of the incident light, so that which position of the photodetector the light beam is incident to is detected on the basis of the output signal of the photodetector. The sunshine which is incident from the oblique direction is cut off by a light shielding plate 14.
OOMACHI YOSHIO
TORIHATA SHIGENORI
