In this experiments, two MS-FBG sensors were placed in a hydrogen test chamber: one with its fiber end sealed for pressure sensing and the other with its fiber end kept open for referencing purposes. It could be demonstrated that both sensors show a similar wavelength shift after some time and that due to the hydrogen diffusion, the pressure in the airholes of the sealed MS-FBG sensor equalizes the hydrogen pressure in the chamber. Furthermore, it could be demonstrated that the refractive index seen by the waveguide of the fiber is also affected. Based on all these observations, the influence of the hydrogen on the temperature and pressure measurement performance of the MS-FBG sensor is estimated, and a mitigation scheme that partially compensates for this influence is discussed.
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Ji-Ying Huang, Jan Van Roosbroeck, Johan Vlekken, Damien Kinet, Antonio Bueno Martinez, Thomas Geernaert, Francis Berghmans, Bram Van Hoe, Eric Lindner, Christophe Caucheteur, "Micro-structured fiber Bragg grating based pressure sensors in a downhole-like hydrogen rich environment," Proc. SPIE 10680, Optical Sensing and Detection V, 106800L (9 May 2018);