Patent ID: 7554671
Filing Date: 2009-06-30
Classification: G01B

Abstract:
1. An absolute position measurement apparatus comprising: a first light source configured to emit a first beam having high coherence; a second light source configured to emit a second beam having low coherence, the second beam having a central wavelength difference from the central wavelength of the first beam; a multiplexing unit configured to multiplex the first beam and the second beam onto the same optical axis to obtain a first multiplexed beam; a polarization beam splitting unit configured to split the first multiplexed beam from the multiplexing unit into a second multiplexed beam and a third multiplexed beam, and to multiplex the second multiplexed beam reflected from a measurement reflection plane of an object and the third multiplexed beam reflected from a reference surface; a wave plate allowing the first beam of the second multiplexed beam and the first beam of the third multiplexed beam to interfere with each other, and allowing the second beam of the second multiplexed beam and the second beam of the third multiplexed beam to interfere with each other; a light-receiving unit configured to detect a first interference beam obtained from a first beams and a second interference beam obtained from the second beams; and a calculation unit configured to determine the position of a measurement origin for the measurement reflection plane by using the interference intensity of the second interference signal obtained from the second interference beam at the light-receiving unit and the phase difference of the first interference signal obtained from the first interference beam at the light-receiving unit and the second interference signal and to obtain the absolute position of the object on the basis of the position of the measurement origin.