A novel multifunctional optical fiber sensor based on FBG and fiber optic coupler

This paper introduces a novel multifunctional fiber sensor with two FBGs (measuring temperature and strain simultaneously) and a fiber optic coupler (monitoring the damage of composite) for structural health monitoring. Two FBGs with different wavelengths are abreast connected to an optical splitter: One is capsulated in glass capillary tube to measure temperature and not affected by strain, the other one is to measure temperature and strain. The other port of the former FBG is connected to the fiber optic coupler, using the transmission intensity in grating for structural health monitoring (SHM) of composite materials. It is pivotal to discriminate the variable of it caused by temperature and strain, as the wavelength of FBG varies with temperature and strain simultaneously. The technique is designed for distinguishing strain and temperature to solve the cross sensitivity problem in this paper. A series experiments demonstrate that the novel multifunctional optical fiber sensor possesses high sensitivity and high precision. With composite materials being used widely in aerospace engineering, national defence, civil engineering, oil field and etc, monitoring the damage of them is more important regarded. The temperature and strain affect the damage of composite materials mostly. Combined with the AE events, according to the temperature and strain of composite materials, the sensor can confirm whether they are demolished and how intensity they are damaged.