Issues and characterization of fiber Bragg grating based temperature sensors in the presence of thermal gradients

This paper reviews the main issues arising from the use of fiber Bragg gratings as temperature sensors in the presence of significant thermal gradients. These conditions occur for example during laser thermal ablation of tumors. In particular, the paper focuses on the identification of the grating position along the fiber, which represents one of the main uncertainty contributions. A novel experimental setup for the grating center localization is proposed and the corresponding characterization procedure has been devised. The setup is built in such a way as to generate reproducible linear temperature distributions. Tests carried out using a sensor prototype have shown that the grating position can be found with a standard uncertainty of 0.3 mm.