Chinese Optics Letters, Vol. 17, Issue 11, 110604 (2019)
Improvement on refractive index sensing by exploiting the tapered two-mode fibers
Fang Fang1, Bing Sun1,*, Zuxing Zhang1,**, Jing Xu2, and Lin Zhang3
- 1Advanced Photonic Technology Laboratory, College of Electronics and Optical Engineering & College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
- 2Optical Communications Laboratory, Ocean College, Zhejiang University, Zhoushan 316021, China
- 3Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET, UK
The spectral characteristics and sensitivities of a tapered two-mode fiber sandwiched between two single-mode fibers are systematically investigated. Theoretical calculations reveal that a dispersion turning point (DTP) appears when the group effective refractive index (RI) difference between the fundamental mode and the higher-order mode equals zero; as a result, ultrahigh RI sensitivities can be achieved. Furthermore, the location of the DTP is strongly dependent on the tapering condition. Then, we experimentally demonstrate high sensitivities of the RI sensor with the waist diameter of ～4 μm by means of immersing it in a flow cell filled with glycerol solution. In further tracking of the resonant wavelength shift around the DTP, it is found that the proposed RI sensor exhibits a sensitivity of 1.81 × 104 nm/RIU and a limit of detection down up to 3.29 × 10 5 RIU in a liquid glycerol solution.