A hybrid fiber-optic sensing system for down-hole pressure and distributed temperature measurements

• A hybrid fiber-optic EFPI/ DTS sensing scheme is proposed.
• A laser diode is the common light source of the hybrid sensing system.
• Alternative measurement by adjusting the injection current of a laser diode.
• No crosstalk between the spectral range of EFPI sensor and DTS.
• Pressure measurement can be compensated by measured temperature values.

A hybrid fiber-optic sensing technique, combining the extrinsic Fabry–Perot interferometer (EFPI) based pressure sensor with the incoherent optical frequency domain reflectometry (IOFDR) based distributed temperature sensor (DTS), is presented for down-hole measurements. By using a laser diode as the common light source, a highly integrated hybrid EFPI/DTS sensing system has been developed with a single fiber. With the injection current of the laser diode below lasing threshold, the broadband spontaneous emission light is used for EFPI based pressure sensing; while with the injection current above the threshold, the stimulated emission light is used for Raman based distributed temperature sensing. There is no overlap between the spectral range of the reflected light from the EFPI sensor and the spectral range of the Raman scattered light. Pressure and distributed temperature can thus be measured by using wavelength-division multiplexing (WDM) technology. Experimental results show that both the pressure and the distributed temperature are measured with little interference. Furthermore, the pressure measurement can be compensated by the measured temperature values.