Impact of high UV fluences on the mechanical and sensing properties of polymer optical fibers for high strain measurements

Abstract

PMMA-based fibers are widely studied for strain measurements and show repeatable results for Fiber Bragg Gratings (FBGs) inscribed using 325 nm laser and 248 nm laser. However, there is no available material mechanical behavior characterization of the UV source impact on the fiber properties. In this manuscript, fibers are irradiated with high fluence of 325 nm and 248 nm lasers and the fibers properties are investigated using dynamic mechanical analysis and tensile strain for potential use of these fibers past the yield point. It is demonstrated that the UV sources shifted the ultimate tensile strength and changed the strain hardening behavior. Tensile strain measurements show excellent repeatability for gratings inscribed with these two sources with similar sensitivity of 1.305 nm/mε for FBG inscribe with 325 nm laser, and 1.345 nm/mε for grating written with 248 nm laser in the range 0 to 1.5 % elongation. Furthermore, tests far beyond the yield point (up to 2.8 % elongation) show that grating inscribed with lower UV wavelength exhibit hysteresis. Finally, we demonstrate that 248 nm laser fluence shall be chosen carefully whereas even high 325 nm laser fluence do not critically impact the sensor properties.

Influence of Annealing on Polymer Optical Fiber Bragg Grating Inscription, Stability and Sensing: A Review

“…Therefore, annealing process could influence the properties of polymers [42,43], and further influence the inscription, stability and application of gratings [16,37,39,44]. In addition, in PMMA-based POFs, photosensitive materials, such as trans-4-stilbenemethanol (TS) [45,46], benzyl dimethyl ketal (BDK) [47] and diphenyl disulphide (DPDS) [48,49] were doped in the fiber core to improve the grating inscription efficiency [50][51][52][53]. However, in some cases, the gratings were not stable, showing a decay performance.…”

High-sensitivity, high-spatial-resolution distributed strain sensing based on a poly(methyl methacrylate) chirped fiber Bragg grating

“…Among these materials, PMMA was the preferred material for producing POF because of its relative ease of fabrication, high optical transparency in the visible region, and refractive index similar to that of a conventional silica optical fiber [14]. CFBGs in PMMA-based optical fibers are promising sensing devices owing to their fundamental mechanical advantages over silica fibers (73 GPa) including a lower Young's modulus (2.3 GPa) [15], higher elastic limit, simple installation in a narrow space, and improved biocompatibility for sensing applications [16]. Min et al and Marques et al have reported that the PMMA-based CFBG can be used as an average strain sensor with a good sensitivity [17,18].…”