A hybrid sensing system for simultaneous Raman-based distributed and FBG-based quasi-distributed measurements

• A novel hybrid fiber-optic Raman/FBG sensing scheme is proposed.
• A laser diode is the common light source of the hybrid sensing system.
• Simultaneous Raman-based distributed and FBG-based quasi-distributed measurements.
• No crosstalk between the spectral range of DTS and FBG sensors.
• A capability of high-capacity multiplexing for FBG sensors.

A hybrid sensing technique, combining the incoherent optical frequency domain reflectometry (IOFDR) based Raman distributed temperature sensor (DTS) with high-reflective fiber Bragg grating (FBG) sensors, is presented for simultaneous distributed and quasi-distributed measurements. By using a laser diode as the common light source, a highly integrated hybrid Raman/FBG sensing system has been developed with a single fiber. The stimulated emission light and the spontaneous emission light of the laser diode are used for DTS and FBG interrogations, respectively. There is no overlap between the spectral range of the Raman backscattered light and the spectral range of the reflected lights from the FBG sensors. The distributed and quasi-distributed measurements can thus be achieved simultaneously by using the wavelength-division multiplexing (WDM) technique. Experimental results show that, both the distributed temperature and the quasi-distributed temperature or dynamic strain can be measured with little interference. Furthermore, the hybrid system shows the capability of high-capacity multiplexing for FBG sensors.