Radiation tolerant FBG thermo-hygrometers for relative humidity detection in the CMS experiment at CERN

This work investigates the performances and the radiation tolerance of optical thermo-hygrometers based on Fiber Bragg Gratings (FBG) technology for humidity monitoring in the Compact Muon Solenoid (CMS) experiment at CERN, in Geneva. Extensive characterizations in terms of sensitivity, repeatability and accuracy on 80 specially produced polyimide-coated FBG sensors and 80 commercial temperature FBG sensors are presented. Progressive irradiation campaigns with γ- ionizing radiations were also performed. Results showed that the sensors sensitivity is unchanged after each radiation exposure; while the wavelength peak exhibits a radiation-induced shift. The saturation properties of this shift are discussed.