A fiber ring cavity laser sensor for refractive index and temperature measurement with core-offset modal interferometer as tunable filter

In this paper, a fiber ring cavity laser refractive index (RI) and temperature sensor is presented. A core-offset Mach-Zehnder (MZ) interferometer is utilized as a sensing element as well as a filter. The core-offset distances of these two joints fabricated by a common fusion splicer are about 3.7 μm, which well ensure the robustness and tensile strength. The directions of these two offsets are unnecessary to be controlled since low fringe visibility is acceptable in this sensor. The Erbium doped fiber (EDF) ring cavity laser setup is helpful to improve the spectral quality factor Q and the detection limit (DL). The Q value of this laser sensor can be higher than that of ordinary core-offset sensing structures by two magnitudes. By combining the core-offset MZ interferometer with EDF ring cavity laser, the final calculated detection limits for temperature and RI measurement are 0.35 °C and 4.54 × 10−4, which are 10 times higher than those of the individual MZ interferometer. The proposed sensor possesses the advantages of low cost, simple operation and easy fabrication process.