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In this paper, we have demonstrated birefringence modification in regenerated grating in polarization maintaining fiber (RGPMF) by using a CO2 laser annealing technique. After conducting an isothermal annealing procedure followed by a slow cooling process, the birefringence of the RGPMF has been increased. This phenomenon can be explained by the changes in the thermal expansion coefficient and glass transition temperature of the stress applying part at different cooling rates. This process was reversible by reannealing with a subsequent fast cooling process. In our observation, the birefringence exponentially increases with a decreasing cooling rate. The highest and lowest records in the birefringence throughout the annealing process are 4.72 × 10-4 and 3.46 × 10-4, respectively (a difference of 1.26 × 10-4). This finding is useful for the study of the birefringence modification, measurement range, sensitivity, and accuracy of PMF or PMF-related devices.

In this letter, a pair of regenerated gratings with Bragg wavelengths of 1547 and 1304 nm in a single piece of singlemode fiber has been fabricated for simultaneous monitoring of temperature and strain in ultrahigh temperature environment. A 3 × 3 matrix is used to characterize the cross sensitivity of the proposed sensor in which the strain sensitivity varies with temperature change. The proposed structure exhibits the deviation of 28.3 με and 4.1 °C at the ranges of 0-1000 με and 25 °C- 900 °C, respectively. [ABSTRACT FROM PUBLISHER]