提出一种基于纳米膜涂覆的外包层腐蚀双包层光纤(DCF)复合结构传感器。该结构可以通过调控腐蚀时间和纳米膜涂覆厚度来改变传感器的耦合模式、谐振波长、最佳折射率传感区间等传感器参数。理论分析了DCF外包层厚度减小时，DCF模式耦合特性以及折射率传感灵敏度的变化情况。实验中通过在外包层直径为59 μm的DCF上涂覆2000层的Al2O3纳米膜，实现了在1.336~1.356折射率范围内1200 nm/RIU的灵敏度(RIU为单位折射率)，这是未经腐蚀和涂覆DCF的24倍。该传感器具有灵敏度高、一致性好、耦合模式可控、传感器参数可定制化等优点，有望在生物医学和化学检测等领域有极大的应用价值。

We propose a sensor based on etched double-cladding fiber (DCF) coated with nanofilm. The coupling mode, resonant wavelength and the best sensing interval can be adjusted by control of the etching time and coating thickness. The evolution of mode behaviors and refractive index (RI) sensitivity as DCF cladding thickness decreasing is theoretically analyzed. In the experiment, 2000 layers of Al2O3 nanofilms are coated on a DCF with an outer diameter of 59 μm to achieve a sensitivity of 1200 nm/RIU in the RI range from 1.336 to 1.356, in which RIU is RI unit. The RI sensitivity of proposed fiber is 24 times than that of bare DCF. The sensor has the advantages of high sensitivity, good consistency, controllable coupling mode, and customizable sensor parameters. It is expected to have great application value in biomedicine, chemical detection and so on.