Fiber Bragg grating temperature sensor for practical use.

Fiber Bragg grating (FBG) is a promising measurement technology for future sensor system applications. Little attention has been given to the FBG sensor housing, however it is important that the FBG is embedded in a conventional electrical sensor housing so that it may be installed easily in instrumentation systems. 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 a stainless sheath. Employing a high numerical aperture fiber with polyamide recoating, we have determined that the bending loss of the small radius U-turn fiber and heat resistance is less than 0.1 dB and up to 250 degrees C respectively. The wavelength shift of this sensor due to temperature change is 10.3 pm/degrees C equal to that of general FBG. Consequently the practical use of this sensor has been confirmed.