Accurate calibration on optical axis of polarizer in a polarization imaging system

Division of time polarimeter (DoTP) is one of the popular imaging instruments in several applications because of its simple configuration and accurate performance. However, calibration of the optical axis of the used polarizer is also the premise of an accurate polarimeter. In this paper, a novel on-line and accurate method is proposed to calibrate the transmission angle of the polarizer using a Wollaston prism. The Wollaston prism splits the incident light into two light beams with orthogonal polarization directions, which are vertical and parallel with the beams plane, respectively. Then these two beams pass through the candidate polarizer. The detected light intensity can be adjusted by rotating the polarizer, whose position is marked by a digital encoder. The angle of optical axis of the polarizer relative to the line of points of two light beams can be solved by a series of light intensities. Finally, the optical axis of the polarizer is calibrated on-line, and the state of polarization of incident light can be measured accurately. Numerical simulation and experiments have validated the feasibility of the proposed on-line calibration method. The experimental results show that the calibration accuracy is about 0.0106° with a maximum polarization measurement error of 3.7 × 10^–4. In general, the proposed calibration method is very fast, on-line, accurate, and would be a good reference for polarization imaging and polarization calibration.