| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system displacement measuring apparatus capable of position detection with high resolution. SOLUTION: An image of a coherent light La is formed on the grating surface of a diffraction grating 1, and the image of a diffracted light Lb is formed on the light receiving surface of a light receiving means 3. The optical path lengths of the diffracted light Lb passing the aperture range of a second image forming means 5 are all equal. As a result, even when the optical axis of the diffracted light Lb is deviated, the imaging position of the light receiving surface of the light receiving means 3 is not changed, and change is not generated in the optical path length. The two diffracted lights Lb, in which optical path lengths are not changed are made to interfere with each other, and its phase difference is detected. On the basis of the phase difference, the moving position of the diffraction grating 1 is measured.
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