PURPOSE: To remove direct offset components by dividing a measuring light and a reference light into three beams, processing one of the three lights by a phase modulation, letting the divided measuring and reference lights interfere with each other, introducing a reflecting light of a to-be-measured object into an interferometer, and obtaining a displacement of the object based on a detected output of the interference light. ;CONSTITUTION: Each of an output light from a laser diode 1 as a reference light and a reflecting light from a to-be-measured object as a measuring light is divided into three beams and interfered with each other. A phase shift is executed so as to obtain interference signals of 0°, 90° and 180° phases. Direct current offset components of the interference signals changed by the change of an intensity of the reflecting light at a corner cube 3 and the change of an intensity of the output light of the laser diode 1 are removed by differences of the obtained three interference signals. Since phase shifters 5b and 5c simply shift phases of the interference signals to 0°, 90° and 180°, the sensor responds at high velocity without restrictions by the modulation.;COPYRIGHT: (C)1995,JPO
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