| 摘要 |
PURPOSE: A position detection device is provided to prevent the generation of high-order diffracted light, which is unnecessary for position detection, by using a first diffracted light. CONSTITUTION: A position detection device, which detects a phase change of light caused by the displacement of a diffraction grating(11), comprises a protective layer(12) which is formed to cover a surface, in which the diffraction grating is formed, and has a specified refractive index. The incidence angle(&amp;thgr;0) of coherent light to the diffraction grating is set to meet |sin&amp;thgr;0|<(2λ0/dn)-1. A first diffracted light is used for position detection.
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