为解决传统光纤折射率传感器灵敏度较低的问题,提出一种基于游标效应增强的拉锥光纤耦合器折射率传感器。利用拉锥光纤耦合器的双折射效应,在耦合器中形成x偏振态和y偏振态两路模式(奇模与偶模)干涉,两路略有差别的干涉通过叠加,形成游标效应。通过理论分析和数值计算,发现当拉锥耦合器的宽度为1.6~3.2 μm时,奇模与偶模的群双折射系数差值会出现零点,折射率传感器的灵敏度会得到显著增强。在理论分析和数值仿真的基础上,实验研究了宽度为1.6 μm的光纤耦合器的折射率传感性能,并在折射率1.333附近获得了30020.0 nm/RIU和-34402.5 nm/RIU的超高灵敏度。该传感器制作简单、结构紧凑且成本较低,在高灵敏度生物医学检测和分析化学领域具有重要应用前景。

In this study, we propose an ultrasensitive refractive index sensor based on tapered optical fiber couplers and assisted with the vernier effect to overcome the problem of low sensitivity of the conventional optical fiber refractive index sensors. Two passes of mode interferences between the even and odd modes, can be achieved in both x-polarization and y-polarization by utilizing the birefringence effect of the tapered optical fiber couplers, and the superposition of these two interferences results in the vernier effect. Based on theoretical analysis and numerical calculations, the difference in the group birefringence coefficient between the even and odd modes is observed to denote zero points when the width of the tapered optical fiber coupler is 1.6--3.2 μm, significantly enhancing the sensitivity of the refractive index sensor. Further, we experimentally demonstrate our theoretical results using a tapered optical fiber coupler with a width of 1.6 μm, achieving ultrahigh sensitivities of 30020.0 nm/RIU and -34402.5 nm/RIU near the refractive index of 1.333. Our sensor is easy to fabricate, compact in structure, and cost effective, and it exhibits significant application prospects in the fields of ultrasensitive biomedical detection and analytical chemistry.