Strain and temperature sensors using multimode optical fiber Bragg gratings and correlation signal processing

A novel type multimode fiber optic Bragg grating (MM-FBG) sensor for strain and temperature sensing has been developed for a power-by-light hydraulic valve monitoring system. The Bragg grating sensor was fabricated by the holographic method in 62/125 /spl mu/m graded-index silica multimode fiber. The sensor has reflectivity of approximately 35% at 835 nm of peak wavelength. The experiment of strain sensing has been tested by apply axial strains from zero to 1000 /spl mu//spl epsi/ and the temperature sensing test has been done for temperatures from -40/spl deg/C and 80/spl deg/C. The strain sensitivity of the MM-FBG is 0.55 pm//spl mu//spl epsi/ and the average temperature sensitivity is approximately 6 pm//spl deg/C.