Residual and Induced Birefringence Measurement of ITO-Coated PET Substrate by Photoelastic Method

Indium tin oxide (ITO) coated polyethylene terephthalate (PET) is widely used as the substrate for the flexible electronics and photonic devices and displays. These PET substrates are found to be birefringent due to the residual stress induced during manufacturing process, which may change the optical properties of display devices. In this paper, we report the measurement of the residual and induced birefringence as a function of the bending applied to the PET substrates for red, green, and blue (RGB) wavelengths of laser light. We have used the basic photo elasticity set-up for recording the interference fringes using CCD camera. The recorded interferograms were analyzed from the line profile calculated by the MATLAB program. We found that the change in birefringence for ITO/PET substrate follow the Cauchy's law of dispersion for the different applied curvature, for the RGB wavelengths.