Simultaneous measurement of temperature and infinitesimal displacement using the high cladding mode coupling loss in fiber Bragg grating

A novel application of fiber Bragg grating (FBG) cladding modes for simultaneously measuring infinitesimal displacement alteration and temperature is presented. The above 30-dB high cladding mode coupling loss with 0.1 nm narrow bandwidth can be easily obtained using the photosensitive fiber with hydrogen loading technique. The wavelength shifts and the variations of coupling loss of the narrow resonances facilitate the measurement of infinitesimal displacement change, as well as the central wavelength of fiber Bragg grating can provide the surrounding temperature information. The 25 μm displacement measurement resolution can be obtained if the wavelength interrogator of 1 pm accuracy is used. The temperature sensing resolution can reach around 0.1 °C in the range from 20 to 120 °C.