Optical low-coherence reflectometry for a distributed sensor array of fiber Bragg gratings

An optical low-coherent interferometric technology for fiber Bragg grating (FBG) sensor array is described. A series of identical FBGs with low reflectivity form a sensor array. The first FBG of the array works as the reference FBG and the others work as sensing FBGs. Each sensing FBG and the reference FBG can form an in-fiber Fabry–Perot (F–P) interferometer with a specific cavity length. By scanning a home-made optical low-coherence reflectometry, the interference signals corresponding to different sensing FBGs (F–P interferometers) can be obtained and well distinguished. The mismatch in wavelength between the reference FBG and a sensing FBG induced by the measurand around this sensing FBG will cause the decrease of the intensity of the corresponding interference signal. A measurement of temperature is demonstrated and good performance is achieved. Factors limiting the total number of sensing FBGs are also discussed.