Corrections of Fabrication Errors of Pixelated Polarization Cameras and Their Influences on Photoelasticity Measurement Accuracy

The adoption of pixelated polarization cameras has greatly accelerated photoelasticity measurements and enabled real-time and on-site testing. Undoubtedly, pixelated polarization cameras are critical for modern photoelasticity techniques. Their core design integrates a nano-grating polarizer in front of each pixel on the camera sensor. Nano-grating polarizers are manufactured via advanced micro-nano fabrication techniques. Manufacturing errors, such as non-uniformity in grating pitch and depth distribution, lead to an inhomogeneous distribution of light polarization properties that deviates from the original design specifications and introduces systematic measurement errors. Nevertheless, the influence of fabrication errors on the measurement accuracy of photoelasticity has not been systematically evaluated. In this work, we first verify the existence of manufacturing errors. We then implement a software correction algorithm proposed in the literature to compensate for hardware fabrication errors, and carry out a series of experiments to assess how this algorithm affects the measurement accuracy of a pixelated polarization camera-based photoelasticity. Our results demonstrate that the software correction algorithm achieves significant improvement only for data with a high degree of linear polarization (DoLP). It can restore degraded DoLP values, which are caused by the low extinction ratio of nano-grating polarizers arising from imperfect fabrication, to their normal level. However, the algorithm shows limited correction performance for data with low DoLP or weak stress birefringence. Furthermore, we find that correction parameters cannot be shared among different pixelated polarization cameras, even for cameras from the same manufacturer; calibration and correction must be performed individually. These findings can provide guidance for photoelasticity measurements using pixelated polarization cameras.