Spectral Properties of Locally Pressed Fiber Bragg Gratings Written in Polarization Maintaining Fibers

In this work, we analyze the spectral properties of locally pressed fiber Bragg gratings (FBGs) written into polarization maintaining fibers. We study the evolution of the spectral response of a FBG written into a PANDA fiber when the central region of the grating is perturbed by a diametrical load. Due to the complex structure of the fiber, a finite element model was carried out to determine the strain distributions generated at the center region of the fiber core, and hence taking the induced change in refractive index as the change in effective refractive index due to the applied load. Once the shifting in Bragg wavelength and the optical principal axes of the loaded region are known, a modified transfer matrix method is applied to calculate the spectral response of the FBG. We have found experimentally and by numerical simulations that the reflected spectra for the grating exhibit a narrow and tunable polarization-dependent spectral hole. The tuning of this spectral hole is dependent of the magnitude and the angle of the applied force over the optical fiber.