• Chinese Optics Letters
  • Vol. 17, Issue 11, 110604 (2019)
Fang Fang1, Bing Sun1、*, Zuxing Zhang1、**, Jing Xu2, and Lin Zhang3
Author Affiliations
  • 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
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    DOI: 10.3788/COL201917.110604 Cite this Article
    Fang Fang, Bing Sun, Zuxing Zhang, Jing Xu, Lin Zhang. Improvement on refractive index sensing by exploiting the tapered two-mode fibers[J]. Chinese Optics Letters, 2019, 17(11): 110604 Copy Citation Text show less

    Abstract

    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.

    The growing need for highly sensitive and robust refractive index (RI) sensors engaged in a wide range of fields, especially in biochemical analysis, food safety, environmental monitoring, and industry process monitoring, has driven the study of various sensing schemes. For instance, the monitoring of contaminants and impurities such as preservatives in natural and daily foods is critical in food safety[1]. Also, the measurements of salinity in the aspects of oceanics, marine environment monitoring, seasonal climate prediction, mariculture, and solar engineering are a complex subject. Moreover, there is a need to measure small RI changes in small volumes of liquid in the bio-sensing field. Traditional bulk refractometers are then not appropriate due to their inconvenient size and weight. Among the demonstrated sensing schemes, fiber-optic RI sensors (FORISs) offer distinctive light–matter interactions, along with their unique advantages of compact footprint, short response time, immunity to electromagnetic interferences, and the possibility of distributed sensing[211].

    Copy Citation Text
    Fang Fang, Bing Sun, Zuxing Zhang, Jing Xu, Lin Zhang. Improvement on refractive index sensing by exploiting the tapered two-mode fibers[J]. Chinese Optics Letters, 2019, 17(11): 110604
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