Combined fluorescence decay time and fiber Bragg grating temperature and strain sensing

Bragg grating-based sensor devices are popular as they are relatively simple to fabricate and use, but the need for compensation for temperature effects is of particular importance for accurate and reliable measurement of other parameters. Equally, the use of rare-earth-doped fiber has revolutionized many aspects of both communications and sensor systems and recent research has produced fluorescence decay-time and intensity ratio transducer devices which yield reproducible and accurate temperature measurement. This work reports on research carried out on sensor devices using co-located Bragg gratings and fluorescence decay-time sensors, using both separate optical fibers (plain and rare-earth-doped silica respectively) or with the Bragg grating actually written into the fluorescent fiber. The sensor system thus created is simple and effective with a single optical source used to excite both the fluorescence emission (which provides decay time information) and to enable the measure-induced Bragg grating wavelength shift to be determined. With such systems under test, satisfactory strain and temperature resolutions have been achieved. Applications include temperature compensated structural monitoring and monitoring of temperature in structures where the sensors are exposed to strain.