| 主权项 |
1. A displacement detecting device comprising:
a diffraction grating having a trapezoidal or rectangular relief shape; an irradiation optical system having a light source section configured by a laser diode or a super luminescent diode for emitting coherent light, a lens to cause the coherent light emitted from the light source section to form an image on the diffraction grating, a non-polarizing beam splitter for splitting the light emitted from the light source section into two beams, and two mirrors adapted to reflect the two beams to the diffraction grating, respectively, and adapted to irradiate the two beams onto the diffraction grating as p-polarized light, respective, by rotating the light source section with an optical axis of the emitted light as a rotation center; a reflection optical system that includes two lenses each having a focus position on the diffraction grating, and two mirrors arranged such that two first diffracted lights obtained from the two beams through diffracted by the diffraction grating and passed the lenses are perpendicularly incident thereon, respectively, the reflection optical system being adapted to reflect the two first diffracted lights, and cause the two first diffracted lights to be incident again on the diffraction grating as p-polarized light, respectively; an interference optical system that includes a half-wave plate and a light combiner comprising a polarizing beam splitter, the interference optical system being adapted to cause two second diffracted lights obtained from the two first diffracted lights incident again on the diffraction grating through diffraction by the diffraction grating and reflected by the two mirrors of the irradiation optical system, to interfere with each other so as to obtain interference light, one of the two second diffracted lights being rotated 90 degrees with respect to a polarization direction thereof so as to be s-polarized light by passing the half-wave plate and reflected by the light combiner, and the other of the two second diffracted lights passing the light combiner as p-polarizing light, thereby being combined with each other to be the interference light, the interference optical system including a quarter-wave plate that makes the two second diffracted lights combined with each other by the light combiner to circularly polarized lights with mutually reversed rotational directions, a non-polarizing beam splitter that splits the combined two second diffracted lights into two beams, and two polarizing beam splitters that respectively split each incident beam of the two beams, obtained by splitting the combined two second diffracted lights, into an s-polarized component and a p-polarized component; a light receiving section that includes photodiodes, the light receiving section being adapted to receive the interference light obtained in the interference optical system, the photodiodes respectively receiving the s-polarized and p-polarized components of the two beams, obtained by splitting the combined two second diffracted lights in the interference optical system, and obtaining respective current signals; and a position information detecting section having I/V converters that convert the current signals obtained by the photodiodes into voltage signals, amplifiers that amplify the voltage signals converted by the I/V converters, A/D converters that convert the amplified voltage signals to digital signals, and a processor that processes the inputted digital signals and outputs the processed signals as two phase increment signals, the position information detecting section being adapted to detect position information of the diffraction grating based on the two phase incremental signals, wherein: a periodic structure of the relief of the diffraction grating is no more than 1.5 times a wavelength of the coherent light incident on the diffraction grating, and D/Λ=0.7-0.9 when Λ represents a period of a relief of the diffracted grating and D represents a width of a projection of the diffraction grating, the periodic structure of the relief is formed in a two-dimensional direction, and the irradiation optical system, the reflection optical system, the interference optical system, the light receiving section and the position information detecting section are provided for each direction of the two-dimensional direction, the reflection optical system causes the first diffracted lights diffracted by the diffraction grating to be incident again so as to form an image at a position different from the position at which the two beams are incident on the diffraction grating, and the irradiation optical system, the reflection optical system, the interference optical system, and the light receiving section provided for each direction of the two-dimensional direction are arranged so that a line connecting two points different in one direction of the two-dimensional direction, at which light is irradiated by the irradiation optical system and the reflection optical system provided for the one direction of the two-dimensional direction and a line connecting two points different in the other direction of the two dimensional direction, at which light is irradiated by the irradiation optical system and the reflection optical system provided for the other direction of the two-dimensional direction, cross each other. |
