PURPOSE: To reduce the number of optical elements and to make an apparatus light- weight, compact and to enable mass production with the present processing techniques, by dividing a beam of light into two at two surfaces of a plane parallel plate and by causing the two beam to interfere with each other.
CONSTITUTION: Light from a light source 1 is converted to a parallel beam L0 by a lens 2 and enters a plane parallel plate 3, forming beam L1-L4. The beam L1 is a portion of the beam L0 which passes surface A, B, and the beam L2 is light passing the face A, reflected at the face B and further reflected at the face A to pass through the face B. The beam L3 is reflected light from the face A. The beam L4 is light emerging from the face A after passing through the face A and reflected at the face B. The beams L1, L2 are condensed by a lens 4 turned to electric signals by a first photodetector 5. Similarly, the beams L3, L4 are changed to electric signals by a second photodetector 7. Since the beam L2 is reflected twice by the plane parallel plate 3, the optical path is longer than that of the beam L1, resulting in a phase difference. The interference of the beams can be accordingly detected by the intensity, strong or weak of the electric signals of the photodetector 5. The same gone true for the detector 7. Since the lights are made to interfere with each other within the plate 3, the lights are not affected by the fluctuation of the outside air.
NAKADA YASUO
MIYAKE TAKAHIRO
KAMIYAMA TETSUO
SATO HIDEO
KURATA YUKIO
