Multi-functional double rare-earth-doped ball sensor based on a hollow-core microstructure fiber

In this Letter, we demonstrated an ∞-type multi-functional sensor through splicing double rare-earth-doped balls (REDBs) with a hollow-core microstructure fiber. Utilizing the different thermal expansion and thermo-optic coefficients of silica and rare earth, the interference of REDBs will be more sensitive to temperature. On both ends of the dual-ball, we spliced the anti-resonance fiber (ARF) to satisfy the broad waveband transmission. In addition, the special anti-resonance loss peak of the ARF can make the amplitude change of the signal more obvious. The experiments prove that a multi-functional sensor is capable of detecting versatile parameters, such as the illumination response, liquid concentration, and ambient temperature. In addition, the temperature sensitivity can reach 1 nm/°C, and the illumination response is obvious. We also analyze the concentration of P-Methylthiophenol, a substance harmful to human beings in the environment. Its resolution can reach 3.125E-5 mol/L. These results indicate that the sensor can be used in underground mine detection, environmental monitoring, and so on.