Simultaneous measurements of distributed temperature and discrete strain based on Hybrid Raman/FBG system

Abstract

A hybrid optic fiber system is proposed and experimentally demonstrated, which combines the Raman-based distributed temperature sensing (DTS) and high-reflective fiber Bragg grating (FBG) sensors for discrete static strain measurement along the same sensing fiber. A distributed feedback laser (DFB) is adopted to generate stimulated emission (STE) light pulses for demodulation of optical time domain reflectometry (OTDR) technology, and an erbium-doped optical fiber amplifier (EDFA) is utilized to increase the power of laser and produce spontaneous emission (SPE) lights. Thus the STE light is employed as pump light for temperature demodulation through Raman-based DTS, as well the SPE lights can be used for discrete strain demodulation through wavelength division multiplexing of FBGs. Since the central wavelengths of FBGs are far away from the lasing wavelength of the laser, the FBG-induced insertion loss can be negligible, therefore the lights reflected by FBGs have little influence on the performance of DTS system. The strain information can be obtained through deducting the temperature induced wavelength shifts of FBGs, since the temperature information can be achieved by DTS system in advance. The experimental results show the maximum measurement error of temperature and strain are 0.48 °C and 10.47 με, respectively. This hybrid system indicates an effective improved multiplexing scheme based on the Raman-based DTS for simultaneous measurements of distributed temperature and discrete static strain, and a better solution of cross sensitivity problem in FBGs.