The Interrogation of Quasi-Distributed Optical FBG Sensing System Through Adopting a Wavelength-Tunable Fiber Chaotic Laser

Wavelength scanning- and optical time domain reflectometer (OTDR)-based methods have been widely used as sensor interrogation schemes for quasi-distributed fiber Bragg grating (FBG) sensing systems. However, wavelength scanning based technique mainly provides the information of wavelength shift at each FBG sensor, whereas it does not have the locating ability. For OTDR-based technique, the spatial resolution is typically several meters, which is not sufficient for high-resolution sensor locating where a centimeter resolution is usually required. Moreover, both of these two interrogation techniques lack the ability of real-time fiber fault monitoring. To address these problems, a novel interrogation technique for quasi-distributed optical FBG sensors based on a wavelength-tunable fiber chaotic laser is proposed and experimentally demonstrated. In the proposed technique, the wavelength shift at each FBG sensor can be obtained through differentially calculating the cross-correlation peaks at two separate wavelength of input light. The positions of FBG sensors can also be determined by the delay time of the corresponding cross-correlation peak. The proposed technique has the advantages of wide wavelength tunable range (40 nm in our works), tunable strain-sensing sensitivity, stability against source power fluctuation, and capability of interrogating both identical and wavelength division multiplexing-based FBG arrays. Strain sensing experiments show a sensitivity of up to 0.0076 dB/με in the range of 0~1200 με with a good linearity. At the same time, a spatial resolution of 18.86 cm is demonstrated in the real-time fiber fault monitoring, which can be further improved with a higher sampling rate.