Liquid crystal variable retarders (LCVRs) are the core component for rapid and high-precision broadband polarization detection. Additionally, the ability to suppress noise greatly affects the results of polarization measurements. In this work, a solving optimal design approach is proposed for building a high-performance broadband Stokes polarimeter based on LCVRs, which greatly reduces the influences of data fluctuation from liquid crystals and dispersion on the experimental results. This method relies on evaluation criteria of the condition number (CN) to build a gradual optimization that includes the following three steps: fixing the fast axis angles, meeting the requirements of a wideband, and ensuring a minimum CN. Additionally, with the method of increasing the measurement analysis vector, we ensure the whole band in the low CN and offer a solution to the problem of the difficulty in optimizing the LCVRs caused by the large change of retardance at 490–700 nm. Finally, the rapid and high-precision Stokes measurement of 490–700 nm wavelengths is achieved. We test the performance of the polarimeter after optimization in our simulation and experiment, which shows that the total RMS error is less than 0.032 and the single point error is small. This work not only reduces the influence of LCVR error on the experimental results but also makes it possible to apply LCVRs to 490–700 nm detection.
Depolarization and linear-retardance are the increasingly interesting polarization characteristics for disease diagnosis in clinic and scientific study. They can not only be obtained by Mueller polarimetry normally, but also the Stokes polarimetric imaging. Stokes polarimetric imaging with circularly polarized illumination can provide the main optical properties of tissues with a simpler device in a shorter time, which is much more attractive. Unfortunately, it is difficult to realize the standard circularly polarized illumination actually in experiments. In this paper, we establish a theoretical model to display the relationship between the nonstandard circularly polarized illumination and the accuracy of the measurement results. Compared to the measurement results by Mueller polarimetry, we found that the depolarizations measured are the same but retardances measured are not. And except the influence of the nonstandard circularly polarized illumination, the sample’s optical characteristics also affect the accuracy of the measured retardance. Additionally, we have conducted a comparative experiment between Mueller polarimetry and the Stokes polarimetric imaging to verify. According to the simulation and experiment, we have confirmed that Stokes polarimetric imaging has good performance in measuring most samples and broadband detection, but there is a large error for measuring strongly birefringent samples. Our work quantitatively analyzes the effect of nonstandard circularly polarized illumination on the accuracy of Stokes polarimetric imaging through theoretical derivation for the first time. It enriches the error theory of Stokes polarimetric imaging with circularly polarized illumination and lays a foundation for the improvement and application.
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