System and method for detecting the relative positional deviatio

Details System and method for detecting the relative positional deviatio System and method for detecting the relative positional deviatio

1994-10-26

1997-04-29

Turner, Samuel A.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356356, 356363, G01B 902

Patent

active

056254539

ABSTRACT:
A deviation detecting system for detecting a relative positional deviation between first and second diffraction gratings, includes a light source, an illuminating device for projecting first and second light beams from the light source, having different directions of polarization, onto the first and second diffraction gratings along different directions, a first signal detecting device for detecting a first interference light signal from the first diffraction grating, being based on a combination of diffraction light of the first light beam and diffraction light of the second light beam, a second signal detecting device for detecting a second interference light signal from the second diffraction grating, being based on a combination of diffraction light of the first light beam and diffraction light of the second light, a first phase difference detecting device for detecting a phase difference between the first and second interference light signals and, a second phase difference detecting device for producing third and fourth interference light signals for correction of a phase error involved in the detected phase difference, and for detecting a phase difference between the third and fourth interference light signals. The phase error is produced by the first and second diffraction gratings which affect the phase in dependence upon the state of polarization of light impinging thereon. Also provided is a determining device for determining the relative positional deviation between the first and second diffraction gratings on the basis of a phase difference as detected by the first and second phase difference detecting device.

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