Finite Element Stress Analysis of Optical Fiber due to Mechanical Expansion of Hydrogel Coating

Abstract

This paper presents the stress analysis in optical fiber due to swelling of hydrogel material coated on it. The silica optical fiber was assumed to be coated by hydrogel that consists of hydroxyethyl methacrylate, acrylic acid and ethylene glycol dimethacrylate as crosslinker. The hydrogel swelling was modeled using free energy function. The conditional equilibrium of hydrogel was solved using finite element method and the stress induced in optical fiber was simulated simultaneously. The simulations were done for two hydrogel coating thickness values, 30 µm and 40 µm. Etched optical fiber coated by 40 µm hydrogel was also simulated. The results show that maximum stress in optical fiber is higher for thicker hydrogel thickness and is higher for etched optical fiber. Maximum stress magnitudes at all pH values are below tensile strength of optical fiber.

Study on sensitivity improving of fiber Bragg grating based pH sensor

“…Recently, a new kind of chemo-mechanicaloptical sensors based on the FBG has been proposed and studied for the measurement of one of the most important chemical parametersthe pH value of solution, in which the expanding or contracting in the volume of pH sensitive hydrogel coated on the FBG will result in shifts of the reflection spectrum of the FBG. Initially, I. Yulianti [2][3] proposed and studied the FBG-based pH sensor by using two aluminum disks attached at the end of the sensing region to prevent the axial expansion of pH-sensitive hydrogel coated on the FBG. In this design, the structural complexity is introduced, and the measurement range is limited for the poor acid and alkali resistance of aluminum disks.…”

Sensitivity improvement of a fibre Bragg grating pH sensor with elastomeric coating

“…As a result, the stress induced in the hydrogel will produce higher pressure on the fibre and consequently higher strain. A hydrogel coated FBG pH sensor with etched fibre was previously investigated [16]; however the sensitivity improvement is still low.…”