Fiber Bragg grating interrogation technique for remote sensing (100km) using a hybrid Brillouin-Raman fiber laser

Abstract

We propose and demonstrate the feasibility of a novel Fiber Bragg Grating interrogation technique for remote sensing based on the use of a hybrid Raman-Brillouin fiber laser configuration. The laser comprises 100 km of standard singlemode fiber (SMF) in a linear cavity configuration with four Fiber Bragg Gratings (FBGs) arranged in series. The FBGs are used both for the sensing function and for the selection of the lasing wavelengths. A wavelength-swept laser pumps Brillouin gain in the fiber cavity, which is previously set just under lasing threshold by the Raman gain. Furthermore, the sensor signal is detected in the radio frequency domain instead of the optical domain so as to avoid signal to noise ratio limitations produced by Rayleigh scattering. Experimental results demonstrate that the shift of the Bragg wavelength of the FBG sensors can be precisely measured with good signal to noise ration when the FBG are used for temperature sensing.