The changes of birefringence in Type I-infrared (Type I-IR) and Type II-IR fiber Bragg gratings induced by an ultrafast-IR laser in SMF-28 fibers are examined after and/or during grating inscription. The gratings are then annealed at increased temperatures up to 800 °C, and their polarization properties are monitored. It is shown that the birefringence in Type I-IR gratings inscribed in hydrogen (H<sub>2</sub>)-loaded fibers is small (~10<sup>-6</sup>) and can be decayed at room temperature, while the birefringence in Type I-IR gratings inscribed in non-(H<sub>2</sub>)-loaded fibers is relatively higher (~10<sup>-5</sup>) and shows strong dependence on the polarization of the IR laser beam. It has the same annealing resistance as the induced index. For Type II-IR gratings, the birefringence is an order of magnitude higher than in Type I-IR gratings (~10<sup>-4</sup>) and shows strong temperature variation during annealing.
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