Simultaneous Measurement of Stress, Temperature and Refractive Index Using an PMFBG Cascaded with an LPG

This study proposes a new fiber sensor based on the cascaded different types of fiber gratings for applying in the simultaneous measurement of stress, temperature, and refractive index. The fiber sensor is composed of a concatenated the fiber Bragg grating fabricated in polarization maintaining fiber (PMFBG) and the long period fiber grating (LPG) fabricated in photosensitive fibers. The sensing mechanism is based on the variation both of the power in the reflection wavelength and the Bragg wavelength corresponding to the Bragg peaks to be located on the positive or negative slope of the loss peak of LPG. Thus, it can be used for detecting the changes of stress, refractive index, and temperature simultaneously by monitoring the wavelength shift and power variation of PMFBG.