| 摘要 |
PROBLEM TO BE SOLVED: To obtain the optical displacement measuring instrument which can perform stable position detection with high resolution. SOLUTION: The optical displacement measuring instrument 40 has optical paths of two coherent lights La1 and La2 formed obliquely to the direction perpendicular to the grating surface 11a of a diffraction grating 11, i.e., on a slanting surface m2, and irradiates the same point on the said grating surface 11a with the two coherent lights La1 and La2. Then this optical displacement measuring instrument finds the phase difference between two diffracted lights Lb1 and Lb2 generated by the two coherent lights La1 and La2 to detect the relative movement position of the diffraction grating 11.
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