Patent ID: 9612104
Date: 2017-04-04
CPC Classifications: G01B,G01D

Claim:
1. A displacement detecting device, comprising: a light source that emits light; a light-beam splitting section that splits the light emitted from the light source into a first light beam that enters a member to be measured and a second light beam that serves as a reference light; a reflection/transmission section that transmits or reflects the first light beam in accordance with a polarization direction of the first light beam, and causes the first light beam to enter the member, after the first light beam has entered the reflection/transmission section; a phase plate that changes a polarization direction of the first light beam; a reference reflection section that reflects the second light beam; a transmission-type diffraction grating that diffracts the first light beam reflected by a surface to be measured of the member to be measured, and causes the diffracted first light beam to enter the reflection/transmission section again; a light-beam combining section that combines the first light beam diffracted by the diffraction grating with the second light beam reflected by the reference reflection section; a light-receiving section that receives interference light of the first light beam and the second light beam combined by the light-beam combining section; and a relative position information output unit that outputs information on displacement of the surface to be measured in a height direction based on an intensity of interference light received by the light-receiving section, wherein when the member is at a reference position, the reflection/transmission section causes the first light beam to enter the member at a specific point on the surface to be measured, and to be reflected by the surface, and when the first light beam reflected by the surface to be measured is diffracted by the diffraction grating and is caused to enter the reflection/transmission section again, the reflection/transmission section reflects the diffracted first light beam and causes the diffracted first light beam to enter the member at the same specific point on the surface to be measured, again, such that an optical path of the first light beam caused by the reflection/transmission section to enter the member to be measured at the specific point on the surface to be measured of the member to be measured, again and reflected again by the surface to be measured of the member matches with an optical path of the first light beam caused by the reflection/transmission section to enter the member to be measured at the specific point on the surface to be measured of the member to be measured to be thereby reflected by the surface to be measured of the member for the first time.