Temperature monitoring system based on fiber Bragg grating arrays with a wavelength rinable OTDR

Abstract

We have implemented a distributed sensor system based on an array of fiber Bragg gratings (FBGs), which can measure up to 1000 points with a single piece of fiber. The system consists of FBGs having the same resonant wavelengths and small reflectivities (similar to 0.1 dB), and a wavelength tunable optical time-domain reflectometer (OTDR). To interrogate the distributed grating sensors and to address the event locations simultaneously, we have utilized the tunable OTDR. A thermoelectric temperature controller was used to tune the emission wavelength of the OTDR. The operating temperature of the laser diode was changed. By tuning the pulse wavelength of the OTDR, we could identify the FBGs whose resonant wavelengths were under change within the operating wavelength range of the DFB LD. A novel sensor cable with dry core structure and tensile cable was fabricated to realize significant construction savings at an industrial field and in-door and out-door applications. For experiments, a sensor cable having 52 gratings with 10 m separations was fabricated. To prevent confusion with unexpected signals from the front-panel connector zone of the OTDR, a 1 km buffer cable was installed in front of the OTDR. The proposed system could distinguish and locate the gratings that were under temperature variation from 20 degrees C to 70 degrees C.