Long-Period Fiber-Grating Temperature Sensors in Ge-B-Codoped Fibers with Temperature/Strain Discrimination

The temperature-sensing characteristics of long-period fiber gratings were compared for different Ge-B-codoped fibers. The temperature sensitivities varied by one order of magnitude depending on the composition of the core. The temperature sensitivity varied from 0.05 to 0.5 nm/K for the same grating period of 212 mu m. The sensitivities at cryogenic temperatures down to 77 K were also Studied. The strain sensitivities were measured at above the room temperature. Two different loss peaks of a single long-period grating with negative temperature sensitivities and positive strain sensitivities were used to distinguish applied temperature and strain. Discrimination characteristics using a Ge-B-codoped fiber were studied for a strain Of LIP to 4000 mu epsilon.