Using RGB filters and a circularly polarized system to measure the deflection radius of optically anisotropic-polymeric substrates with a sub-grayscale resolution

Abstract

Transparent optically anisotropic substrates (TOASs) are a crucial component in flexible electronics. Moreover, knowing the deflection radii of TOASs is essential to estimate the residual stresses of the thin films deposited on them. This paper proposes a novel measurement method to measure the deflection radii of polyimide (PI) substrates. Red, green, and blue filters and a circularly polarized system were used in the proposed method to investigate the influence of measurement precision on the wavelength of light adopted. Moreover, the image averaging technique was adopted to significantly reduce the noise in the fringe. Thus, the proposed method could be performed using only one set of image information and the measurement resolution could be improved to the sub-grayscale order. The experimental results reveal that red light can be adopted to precisely measure the deflection radii of PI substrates (error of 2.90%) However, large errors are caused when green light is used (22.35%). The experimental results reveal that blue light cannot be used to obtain any interferometric fringe patterns to calculate the deflection radius.