| Heterodyne interferometer is an important optical instrument which is widely used in the precision measurement and positioning,but the nonlinearity errors are the main error for the measurement.This paper studies the relations between nonlinearity errors and optical subdivision numbers in the heterodyne interferometer,it analyzes the non-ideal laser source(including non-orthogonal and elliptical polarization)and the non-ideal PBS.Firstly,the nonlinearity of the two-pass-subdivision and four-pass-subdivision interferometers under the nonideal condition is analyzed by mathematical method,and then it is simulated with MATLAB.The results show that the nonlinearity error is changed with the different subdivision numbers.When the laser beam is non-orthogonal,the nonlinearity errors exist both two-pass-subdivision interferometer and four-pass-subdivision interferometer,and the nonlinearity error in four-pass-subdivision is bigger than two-pass-subdivision interferometer.In another scheme with the ellipticity polarization source,if the two beams source are elliptical polarization with the same ellipse angle,the nonlinearity in four-pass-subdivision is bigger than two-pass-subdivision.However,if only one laser beam exists ellipticity polarization or both laser beams are ellipticity polarization with the different ellipse angles,the nonlinearity in four-pass-subdivision is smaller than two-pass-subdivision.When the PBS is imperfect with the perfect transmission of P polarized only the two-pass-subdivision interferometer causes the nonlinearity,thus it can be seen that the nonlinearity is reduced.But the nonlinearity increases in the imperfect PBS with the perfect reflection of S polarized.Furthermore,if the number of subdivision increases,the nonlinear error increases in the imperfect PBS with the imperfect transmission of P polarized beam and the imperfect reflection of S polarized beam.This study is useful to design the heterodyne interferometer. |
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