2 Method and system for correcting the non-linearity error in a two-frequency laser interferometer

摘要

PURPOSE: A method for measuring a phase angle for measuring length in a two-frequency laser interferometer, and a method for correcting a non-linear error, and a method and a system for measuring a phase angle for measuring length using the same are provided to improve the accuracy of length measurement by correcting periodical non-linear errors. CONSTITUTION: A system for measuring a phase angle includes a two-frequency laser interferometer(100) outputting a reference signal(Ir) generated by interference of two frequency laser flux and a measurement signal(Im) generated by interference of two frequency laser flux reflected from fixed and mobile mirrors(4a,4b); a 90 deg phase mixer(200) mixing the measurement signal with the reference signal and a 90 deg phase converted reference signal each, and filtering high frequency components for outputting output signals(Ix,Iy) for sensing phase; a non-linear error correcting part(300) receiving feedback of output signals(Ix',Iy')for obtaining the amplitudes, and offsets, and phase difference, calculating correction voltage for correcting the amplitudes, the offsets, and the phase difference, and correcting the offsets to become "0", the amplitudes to be equal, and the phase difference to become "0"; and a phase angle calculating part obtaining a phase angle() by applying the output signals to a formula =arctan(Iy'/Ix').