Polarization Properties of Fiber Bragg Gratings and Their Application for Transverse Force Sensing Purposes

Due to the lateral inscription process, Fiber Bragg Gratings (FBGs) written into standard single-mode fiber can exhibit birefringence. The birefringence value is however too small to be perceived in the FBG spectral response but it can lead to significant polarization-dependent properties such as polarization dependent loss (PDL) and differential group delay (DGD). A transverse force applied on the FBG can enhance the birefringence, which increases both the PDL and DGD values. Hence, although these properties are not desired in telecommunication applications, they can be advantageously used for transverse force sensing measurements, allowing the use of FBGs written into standard single-mode optical fiber, which fail to work when they are interrogated through amplitude spectral measurements. This chapter first analyzes the normalized Stokes parameters, PDL and DGD evolutions with wavelength when the FBG parameters and the birefringence value are modified. It then focuses on the realization of a transverse force sensor based on the monitoring of the PDL and DGD evolutions.