Abstract
Metal-coated optical fibers are widely employed in sensing applications owing to their superior mechanical strength and corrosion resistance. However, their calibration at elevated temperatures is hindered by hysteresis, manifested as discrepancies between heating and cooling cycles, primarily caused by residual strain from mismatched thermal expansion coefficients (TECs) between the metal coating and silica cladding. This research introduces an optimal heat treatment procedure aimed at minimizing the impact of the mismatch in TECs between the cladding and the coating materials that causes the residual strain in gold (Au) and copper (Cu) coated fibers for achieving reliable distributed high temperature sensing up to 500 °C using Optical Frequency Domain Reflectometry (OFDR) technology. The treatment facilitates stress relaxation and microstructural modifications, including surface diffusion, grain growth and oxidation (for Cu coatings), which collectively induce partial interfacial delamination and thereby suppress hysteresis. This work presents the first comprehensive experimental study to systematically investigate and demonstrate the mitigation of hysteresis through an optimized heat treatment process and its underlying mechanisms in metal-coated fibers, supported by microstructural insights. The identified treatment range of 25-300 °C achieves substantial reductions in residual strain, lowering hysteresis effects by approximately 90.2% in Cu-coated fibers and 86.6% in Au-coated fibers. Furthermore, Au-coated fibers exhibit a consistently lower degree of hysteresis than Cu-coated fibers under comparable thermal conditions. Heat treatment also enhances temperature sensitivity, with improvements of approximately 28.9% for Cu-coated fibers and 6.6% for Au-coated fibers. Post-treatment strain analysis confirms maximum sustainable strain limits of ∼6000 μϵ for Au-coated fibers and ∼12,000 μϵ for Cu-coated fibers. Both fiber types also demonstrated excellent thermal stability, maintaining consistent performance across three heating cycles between 25 °C and 300 °C over a 20-hour period. Collectively, the findings not only advance the scientific understanding of residual strain relaxation mechanisms but also provide a practical route toward robust, precise, and reliable distributed sensing for demanding industrial environments such as the steel, oil and gas sectors.
Recommended Citation
K. Dey et al., "Mitigating Hysteresis in Metal-Coated Fibers Via Optimized Thermal Treatment for Advanced Distributed High-Temperature Sensing Applications," IEEE Transactions on Instrumentation and Measurement, Institute of Electrical and Electronics Engineers, Jan 2026.
The definitive version is available at https://doi.org/10.1109/TIM.2026.3652753
Department(s)
Electrical and Computer Engineering
Second Department
Materials Science and Engineering
Keywords and Phrases
Distributed temperature sensing; Fiber optic sensors; High temperature sensing; Metal coated fibers; Optical frequency domain reflectometer (OFDR); Thermal treatment
International Standard Serial Number (ISSN)
1557-9662; 0018-9456
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2026 Institute of Electrical and Electronics Engineers, All rights reserved.
Publication Date
01 Jan 2026
