Theoretical and experimental study of structural elements’ influence of fiber-optic strain sensor on its readings and correction procedure for transfer function

Fiber optic sensors (FOS) is a rapidly developing part of measuring equipment. They are regularly expanding their application field in various engineering branches due to high operational properties. A large number of research works are carried out in this field all over the world. Most of the published articles are devoted to the application of FOS and their operating principles in terms of optics and electronics. In the present paper a fiber optic sensor is considered as a mechanical system. A sensor forms its readings while interacting with environment, which is the carrier of the measured parameter. In this process it is possible to distinguish three different aspects that determine the measurement result: the physical (optical) laws underlying the sensor transfer function, the nature of the sensor and environment interaction, and the interaction of sensor structural elements (even in the simplest FOS structure it is possible to distinguish several components with different physical and mechanical properties). All these aspects play a decisive role in the readings formation and must be taken into account by sensor designers. The present study describes the methodology aimed at adjusting FOS transfer function by taking into account all the indicated aspects of the readings formation. A fiber optic strain sensor based on the Bragg grating has been considered as an example. The influence of its structure on the readings has been determined by means of mathematical modeling. The contribution of single structural elements (such as glue, optical fiber, substrate with a technological hole, etc.) to this value has been evaluated. General algorithm for determining the effect of the sensor structural elements in its readings has been formulated as the results’ generalization. The algorithm has been tested using the existing model of the fiber optic strain sensor. The efficiency of the method has been proved by a series of laboratory experiments.