Simultaneous strain and cryogenic temperature measurement by using an improved EFPI/FBG fiber sensor

An improved fiber sensor consisting of a fiber Bragg grating (FBG) and an extrinsic Fabry-Perot interferometric (EFPI) sensor is proposed. The interferometric cavity of the improved sensor is composed of a glass capillary tube and two sections of single-mode fiber (SMF), the segment near one of the SMF's end faces has a FBG. One of the two aligned SMFs is free along the axial direction in the testing specimen, which is different from the traditional structure. During the cryogenic test, only the glass tube and the free SMF with a FBG which exposed outside the glass tube part will be encapsulated by cryogenic adhesives on the testing oxygen-free copper specimen. The temperature and strain performance of the testing oxygen-free copper specimen were studied at high vacuums and low temperatures range 273 K to 30 K. The testing result was agreed well with the theoretical values. The improved sensor is compact, easy in fabrication and has high potentials in cryogenic temperature applications.