Fiber Bragg Gratings in Microstructured Optical Fibers for Stress Monitoring

摘要

Combining the functionalities of fiber Bragg gratings (FBG) and microstructured optical fibers (MOF) offers promising technological perspectives in the field of optical fiber sensors. Indeed, MOFs could overcome some of the limitations of FBGs in conventional fibers for sensor applications. The added value of MOFs stems from the ability to design an optical fiber in which an FBG acts as a sensor with a selective sensitivity, e.g. a sensor that is sensitive to directional strain but not to temperature. For this purpose we use a MOF with a phase modal birefringence on the order of 8×10~(-3), which is more than the double obtained in conventional birefringent fibers. A FBG in this MOF results in two Bragg peak wavelengths, with a wavelength separation that depends on the phase modal birefringence. We characterize these FBGs for transversal loads on a bare fiber and compare the results with simulated sensitivities. Then, we embed the sensor in a composite coupon and we measure the response of the Bragg peak wavelengths as a function of the applied transversal pressure on the composite material. This allows drawing conclusions on the advantages of FBGs in MOFs for sensing applications.