Nanostructured Silver Coatings for Optical Fiber Sensors: Deposition and Morphological Characterization

In the civil and industrial fields, precise control of process parameters is a fundamental requirement to ensure safety and reliability. Sensor technologies provide a wide range of solutions for monitoring chemical and physical quantities. Owing to their immunity to electromagnetic interference, mechanical robustness, and small dimensions, optical fiber sensors—particularly Fiber Bragg Gratings (FBGs)—enable the monitoring of parameters such as temperature and strain even under harsh environmental conditions, ranging from cryogenic temperatures to values exceeding 1000 °C. A crucial aspect of optical fiber performance is related to external coatings, which directly influence mechanical behavior, durability, and compatibility with specific applications. Commercial optical fibers are typically coated with a polymeric layer that provides mechanical protection and facilitates handling. In this work, a nanostructured silver-based metallic coating is deposited via a bottom-up chemical process involving a redox reaction between silver nitrate (AgNO₃) and glucose solutions; its morphological characteristics are investigated. Depositions are performed on bare optical fibers and on fibers coated with polymeric materials, including acrylate, polyimide, and Ormocer®. Through the optimization of process parameters—including pH, temperature, deposition time, and coating thickness—and the study of surface chemical compatibility, the quality of the metallic layers is evaluated for adhesion, uniformity, and homogeneity. The novelty of this work lies in the optimization of a metal deposition approach that is rarely reported for optical fiber coatings. Its application to polymer-coated fibers requires addressing substrates with tailored thermal and chemical resistance, prompting a thorough evaluation of their physicochemical properties to ensure effective metal adhesion and compatibility. Overall, this study contributes to the scientific literature by assessing the potential direct applicability of this method to FBG sensors and by providing a solid foundation for future investigations into sensor performance and the enhancement of measurement capabilities.