Characterization of beam splitters in the calibration of a six-channel Stokes polarimeter

Polarization distortion in a beam splitter is a phenomenon where the polarization state of output light deviates from the theoretical expectation, which is inevitable and will result in significant errors in the optical systems. A theoretical analysis method based on Mueller matrix ellipsometry is proposed for characterizing the beam splitters and the application in the calibration of a six-channel Stokes polarimeter (SP) is shown. In this study, polarization distortions in the beam splitters including depolarization, linear birefringence, circular birefringence, linear dichroism, and circular dichroism have been considered. With the proposed method, the beam splitters are characterized by the polarization distortions and the effective optical parameters extracted. In our experiment, the Mueller matrices of two different commonly used beam splitters measured by a commercial Mueller matrix ellipsometer (MME) are consistently fitted by the proposed method and the residual errors have shown improvement compared to the conventional methods. A practical application of the proposed method is exhibited by calibrating a SP system containing two non-polarization beam splitters and three polarization beam splitters. With the proposed method introduced, the general error of the measured Stokes vector can be reduced from 3% to 1%, and the errors of the thickness measurement of standard SiO2 thin film samples are within 1 nm compared with the results reported by a commercial MME.