Fiber Bragg Grating temperature sensor for practical use

The Fiber Bragg Grating (FBG) is a promising measurement technology for future sensor system applications. Little attention has been given to FBG sensor housing, however it is important that FBG is embedded in the conventional electrical sensor housing to install easily the instrumentation system. We have experimentally fabricated a practical pass-through type FBG temperature sensor which is embedded in the conventional thermocouple housing. A small radius U-turn fiber spliced to the FBG is placed inside the top of stainless sheath. We have determined that the bending loss of the small radius U-turn fiber and heat resistance is less than 0.1dB and up to 250 degrees C respectively, employing high numerical aperture fiber with polyimide recoating. The wavelength shift of this sensor for temperature change is 10.3pm/degrees C equal to that of general FBG. Consequently, the practical use of this sensor has been confirmed.