Bending Radius Determination Using Modified Fibre Bragg Grating Structures

Abstract

The development of novel fibre Bragg grating (FBG)-based bending measurement methods requires comprehensive experimental validation under controlled laboratory conditions. This preliminary stage is essential for verifying the proposed sensing principle, optimising the sensor configuration, and evaluating the interrogation technique prior to implementation in practical applications. Controlled laboratory experiments provide repeatable and well-defined loading conditions, enabling the influence of individual parameters, such as bending radius and temperature, to be investigated independently while minimising the effects of external disturbances. Such investigations facilitate a thorough assessment of sensor performance, including sensitivity, repeatability, and temperature cross-sensitivity, and provide the basis for optimising the sensing system. Consequently, laboratory validation constitutes a fundamental stage in the development of advanced FBG-based bending sensing techniques, significantly accelerating the translation of innovative sensing concepts into engineering and industrial applications. Accordingly, the development of robust and temperature-independent bending measurement methods remains an important area of research. The objective of this work is to present a novel optoelectronic method for determining the bending radius using modified periodic fibre structures. Based on a comprehensive analysis of existing fibre Bragg grating based bending sensing principles and sensor configurations, an original bending determination method employing a modified FBG structure was developed. The proposed experimental configuration comprises a superluminescent diode source, an optical circulator, two optical spectrum analysers, a uniform fibre Bragg grating, and a tilted fibre Bragg grating. Experimental investigations of the spectral response of the combined FBG-tilted FBG (TFBG) structure under various bending conditions and throughout the intended operating temperature range provide the basis for the development of a temperature-independent bending determination method. Prior to implementing the proposed sensing approach, the uniform FBG and TFBG are fabricated in accordance with the specified design parameters, and their spectral characteristics are characterised over the given temperature range. The experimental results are subsequently used to establish design guidelines for selecting the optimal FBG and TFBG parameters to achieve temperature-independent bending sensing.