Optical Study of Humidity Effect on Sol-Gel Glass Chirowaveguide Thin Films and Microstructures

Abstract We present a comprehensive study on the effect of humidity on organically modified sol-gel glasses (ormosils) thin films and related-microstructures, using optical characterization methods. Using a Mach-Zehnder interferometer and a polarimetric setup, we quantitatively measure the variations in refractive index and linear birefringence induced by changes in ambient relative hu-midity. Our findings unveil the high sensitivity of the material’s refractive index to humidity, predominantly attributed to the hygroscopic nature of the polyethylene glycol (PEG) component embedded within the ormosils. Furthermore, We show that stress-induced birefringence during the deposition of the sol-gel layers is partially released in the structured layers compared to the planar one. The remaining stress is reduced by the effect of humidity in a linear relationship in which the proportionality factor is higher in the planar layers. The results shown here shed new light on the complex relationship between humidity and sol-gel derived materials and contribute to the understanding of the mechanisms behind their sensitivity to humidity.