Integrated spectral phase delay calibration technique for a liquid crystal variable retarder used in wide-bandwidth working channel

Abstract

Laser sources with limited wavelengths are commonly used to calibrate the phase delays of liquid crystal variable retarders (LCVRs). However, the parameters describing the phase delays obtained in this manner in certain bands do not match the parameters in the wide-bandwidth working channel employed in polarized imaging detection systems based on LCVRs, which results in deviations in the detection precision. In this paper, we propose an integrated calibration method based on both a multi-band light source and a laser source. The method uses the calibration data obtained by the laser source to correct the calibration data obtained by the light source. The parameters of the phase delays in various spectral channels can be used to precisely measure the LCVR phase delays in the bands of the light source. We conducted experiments to obtain and compare the measured and fitted results for a light source in the 568 nm band. Then, the parameters were used in the instrument matrix calibration of our LCVR based polarized imaging system. The results show that the detection precision of the polarization degree improved more than 0.3% for linear polarized incident light, and more than 0.6% for elliptically polarized light, when our calibration method was applied. These improvements will prove useful in polarizer research, and to improve polarized imaging systems based on LCVRs.