Fast characterization of low-reflectance Bragg gratings in a polarization maintaining fiber using a reference grating

Abstract

A reference grating method for characterizing low-reflectance Bragg gratings in a polarization maintaining (PM) fiber and the corresponding state of polarization (SOP) is presented, and experimentally demonstrated through a fast inline characterization of a PM twin (0.5% + 0.5%) fiber Bragg gratings (FBGs) during the fabrication. The polarization extinction ratio of the pre-set system SOP was determined to be 15.0 dB. The reflectivity measurement for the first grating was carried out while writing the target grating to 1.39%, then in-situ annealing, until after-annealing with a reflectivity of 0.49%. The spectra of the second grating and the combined gratings were characterized by the same way. The combined twin PM FBGs had a bandwidth of 0.515 nm, a center wavelength of 974.304 nm, and a reflectivity of 1.03%. The speed was normally 5 s, and was 3 s without characterizing the system SOP. The reflectivity measurement accuracy was 0.049%.