Metal-coated optical fiber sensors for adaptive structures

Abstract

Adaptive systems modify their configuration in response to the environment, an idea informed by biomimicry. This study reports early-stage development of metal-coated fiber Bragg grating (FBG) sensors for embedding in adaptive structures. FBGs offer a small size, spectral sensitivity, and operation from cryogenic to high temperatures, but bare silica fibers become brittle after polymer removal. To improve robustness and compatibility, we investigated electroless deposition of Cu, Ni, and Ag on 9/125 single-mode fiber. The workflow comprised coating removal, gold sputtering, sensitization/activation, optional polyimide etching, and metal deposition. Copper required Sn/Pd activation to achieve uniform coverage; nickel deposited without activation but produced islanded, weakly adherent films. Tollens’ chemistry plated silver on bare silica and acrylate; etched polyimide supported deposition only within a narrow window (∼2 M KOH, 20 min, 60°C) and remained morphologically non-uniform. Attempts to form an Ag/Ni bilayer failed because the Tollens’-derived Ag underlayer thinned in the alkaline electroless nickel bath, preventing coalescence of a continuous Ni film. This outcome is consistent with Ag–Ni immiscibility, poor catalytic initiation on unactivated Ag, and the chemical/mechanical fragility of thin Ag in ammoniacal media. The results delineate viable metallization routes for resilient, embedded optical sensors.