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

Multimode fiber optic Bragg grating sensors for strain and temperature measurements using correlation signal processing methods have been developed. Two multimode Bragg grating sensors were fabricated in 62/125 mum graded-index silica multimode fiber; the first sensor was produced by the holographic method and the second sensor by the phase mask technique. The sensors have signal reflectivity of approximately 35% at peak wavelengths of 835 nm and 859 nm, respectively. Strain testing of both sensors has been done from 0 to 1000 muepsilon and the temperature testing from -40 to 80degreesC. Strain and temperature sensitivity values are 0.55 pm/muepsilon and 6 pm/degreesC, respectively. The sensors are being applied in a power-by-light hydraulic valve monitoring system.