为了在中红外区域实现气凝胶、七氟醚（麻醉剂重要成分）等物质的折射率检测，拓展折射率检测范围，提出了一种基于双芯光子晶体光纤的表面等离子体共振低折射率传感器.光子晶体光纤由两种大小不同的空气孔围绕中心气孔构成，通过对光纤抛磨，最外侧大空气孔直接与待测物质接触，实现基于金属外涂覆的折射率实时测量.采用全矢量有限元法对该传感器的理论模型进行分析，结果表明，在1.12~1.37折射率范围内，传感器的共振波长位于中红外区域2 505~3 181 nm，最高灵敏度为12 000 nm/RIU，分辨率为8.33×10^-6.该传感器利用中红外波段实现了低折射率检测，并且获得了超宽的检测范围和较高的灵敏度，在化工检测、生物医学传感以及水环境监测等领域具有广泛的应用前景.

In order to realize the refractive index detection of substances such as aerogels and sevoflurane (an important component of anesthetic agents) in mid-infrared spectrum, and expand the detection range of the refractive index, a surface plasmon resonance sensor based on a dual-core photonic crystal fiber for low refractive index detection is proposed. The photonic crystal fiber is composed of two kinds of air holes with different sizes around the central air hole. The outermost large air hole directly contacts the substance to be measured by polishing the fiber, for real-time dectection of refractive index based on metal external coating can be achieved. The theoretical model was analyzed by the full-vector finite element method. The results demonstrate that in the refractive index range of 1.12~1.37, the operation wavelengths of the sensor are in mid-infrared spectrum between 2 505 nm and 3 181 nm. The maximum sensitivity is 12 000 nm/RIU, and the resolution is 8.33×10^-6. The proposed sensor can adopt the mid-infrared band to achieve low refractive index detection, which has obtained a ultra wide detection range and a high sensitivity. It has a board application prospect in chemical detection, biomedical sensing, water environment monitoring and other fields.