The Research On Error Analysis And Optimization Of The Spatially Modulated Imaging Polarimeter

Imaging polarimeter can obtain the 2-D dimension intensity distribution information and its corresponding states of polarization (SOP) information from the target simultaneously. SOP, usually described by the Stokes vector, has the ability to enhance the contrast between the target and the background. Tranditional imaging polarimeters need the mechanical rotating parts for acquiring the full stokes paramters. This inherent property leads the traditional polarimeters to failing in getting the SOP information from the fast-moving objects. The spatial modulated imaging polarimeter equiped with prisms or Savart polariscopes can obtain full Stokes parmaters by a snapshot through an interference pattern. Compared with the divison amplititude polarimeter, the division aperture polarimeter and the division focal plane polarimeter, the spatial modulated imaging polarimeter is easy to be mounting due to its simple mechanism. Therefore, the spatial modulated imaging polarimeter will be widely used in the field of remote sensing, military and biomedicine and so on. In the practical application, the systematic errors will severely influence the polarization measurement precision of the spatial modulated imaging polarimeter. Among the systematic errors, the alignment errors of the rotated half wave plate (HWP) and analyzer are essential and their impacts are non ignorable.Based on the ideal model, the alignment error model has been constructed. In order to estimate the affect of the alignment error, a matrix error model based on the spatial demodulated algorithm is built. Through the Poincare sphere sampling method, different SOPs are chosen as input signals for estimating the impacts of the HWP alignment error, the analyzer alignment error and their coupling error.In order to decrease the impact of the alignment error, an optimization method by using the condition number of the measurement matrix as the merit function has been proposed. This method is trying to get the optimal system from searching for the minimum condition number. Through varying the thickness of the Savart plate, the minimum condition number 2.06 has been found when the thickness is 23mm. The measurement precsions of the system with 6mm,10mm,12mm,23mm and 25mm Savart plate have been estimated. The result shows that 23mm is an optimal design parameter for avoiding impacts of alignment error. However, this method is invalid to the system which only contains the alignment error of the analyzer. According to the consistent norms theorem, it is found that the alignment error of the analyzer is uncorrelated to the condition number of the measurement matrix.For completed verifying if the condition number is effective to improve the performance of the system, the Stokes unit vector method for computing the measurement error has been given. By using this method, the measurement accuracy of the spatial modulated imaging polarimeter can be cacluated only through analyzing the measurement error of the natural light,0°and 90°linear polarized light,45°and 135°linear polarized light and right circularly polarized light and left circularly polarized light.