Analysis and verification of the nonlinear error resulting from the misalignment of a polarizing beam splitter in a heterodyne interferometer

In order to analyze and characterize the periodic nonlinear error resulting from the misalignment of a polarizing beam splitter (PBS) in a laser heterodyne interferometer more accurately, in this paper, starting from the light separating principle of thin-film PBS, we have found that the root cause of the periodic nonlinear error is the frequency mixing induced by the deviation from the Brewster angle of the incident angle or by the rotation of the incident plane when the PBS is misaligned. Moreover, we have established the direct function relationships between the periodic nonlinear error and different PBSs' misalignment errors for the first time. The theoretical analysis shows that the periodic nonlinear error arising from the PBS's yaw error is the largest and the maximal nonlinear errors are unequal even if the positive yaw angle is equal to the negative yaw angle. The nonlinear errors are much smaller under the PBS's roll and pitch errors. The experiments of polarizing leakage and nonlinear error measurement under the PBS's yaw error demonstrate that the experimental results are in agreement with the theoretical analysis.