| 摘要 |
PURPOSE:To simplify structure and to reduce the size of a device by branching laser light to two branch paths through a main waveguide, imposing phase modulation and projecting them on two points of a surface to be detected through an optical convergence system, and making reflected light incident on a photodetector. CONSTITUTION:Light made incident on an incidence path 26B from a light source 23 enter two branch paths 26D and 26E through the main waveguide 26A. Pieces of luminous flux 28A and 28B projected from those branch paths are focused on two points 30A and 30B on a body 29 to be detected while converged through a lens 50. Those reflected light beams come together on the main waveguide 26A through the lens 50 and both branch paths 26D and 26E and enter the photodetector 24A through a projection path 26C. Variation in the quantity of photodetection is converted into an electrical signal. Further, a couple of electrodes 27A and 27B are connected to a power unit 31 and the phases of the light beams traveling in the branch paths 26D and 26E are modulated in the opposite directions by impressing a voltage which varies periodically, so that the outer of the detector 24A varies with the voltage. If there is a difference in level between the light projection points 30A and 30B, the shift in phase between the reflected light entering the branch paths 26D and 26E is measured by a measuring instrument 24B to measure the difference in level on the body 29 to be detected.
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