Patent ID: 8284406

Claim:
A displacement measurement method comprising the steps of: an intensity-modulated beam generation step for generating a beam subjected to intensity modulation at predetermined intervals; an optical interference step for splitting a beam generated by the intensity-modulated beam generation step into first and second beams, irradiating a target mirror provided on a movable object under measurement with the split first and second beams after providing a relative time difference therebetween, combining a reflected beam based on the first beam and a reflected beam based on the second beam, the two reflected beams being obtained from the irradiated target mirror, after canceling the relative time difference, and subjecting the two beams to interference based on an optical phase difference in relation to the unit moving distance of the object under measurement produced during the time difference to generate a plurality of interference light signals; and a calculation step for calculating the unit moving distance of the object under measurement based on the plurality of interference light signals generated by the optical interference step.