Photoenhanced polarization mode separated fiber Bragg gratings inscribed by femtosecond laser

In this paper, we report the fabrication of photoenhanced polarization mode separated fiber Bragg gratings (FBGs) in polarization maintaining (PM) fibers using IR femtosecond laser illumination. The separation of the Bragg resonant wavelengths between the two polarization modes is as large as 1.78 nm due to the photoenhanced birefringence effect generated by the strong ultrashort laser pulses. This large polarization mode separation solves one of the major problems of the conventional PM Bragg gratings (i.e., the narrow spacing or even the partial spectral overlap between spectra of the two polarization eigenmodes) and substantially enhances the multiparameter sensing capability of FBGs by offering a wider sensing range and higher discrimination. Furthermore, the high thermal stability of FBGs (up to 1000 °C for silica fibers) inscribed by IR femtosecond lasers provides for multiparameter sensing in harsh, high temperature environments.