Alignment errors calibration for a channeled spectropolarimeter

This paper presents a method to calibrate alignment errors for a channeled spectropolarimeter. A calibration model, including an alignment errors determination model and an alignment errors compensation model, is derived firstly. To determine the exact alignment errors of the high-order retarders and polarizer included in the spectropolarimeter, an auxiliary high-order retarder and a reference beam are used. The auxiliary high-order retarder does not affect the normal use of the spectropolarimeter and the polarization state of the reference beam needs not to be controlled accurately. Based on the determination results, the alignment errors are compensated by using a correction algorithm without any precise mechanical adjustments. Simulation results show that the alignment errors can be determined accurately and the errors of the reconstructed Stokes parameters due to the alignment errors are reduced effectively by the presented method. Finally, experimental results are summarized and analyzed to demonstrate the effectiveness of the calibration method.