A high-sensitivity square-lattice photonic crystal fiber (PCF) refractive index (RI) sensor based on an external gold coating is proposed. This design eliminates the limitations of selective coating and liquid penetration in the micrometer holes, and avoids the side polishing of D-type fibers. The effects of air hole diameter and gold film thickness on the sensing performance are studied in detail using the full vector finite element method (FV-FEM). In addition, the sensing performance of the gold-coated PCF under the optimized parameters is compared with that of PCF with the same air hole diameter and a gold grating. The results show that the proposed PCF has a higher structural tolerance to the air hole diameter, which improves the manufacturing feasibility. Moreover, the gold-coated PCF has a maximum sensitivity of 31 000 nm RIU⁻¹ and a resolution of 3.23 × 10⁻⁶ RIU in the RI measurement range of 1.34–1.49. The maximum sensitivity of the gold-grating PCF with lower loss is 30 000 nm RIU⁻¹ in the RI detection range of 1.38–1.46, and the resolution is 3.33 × 10⁻⁶ RIU. Low loss is beneficial for extending the length of the fiber, which is convenient for practical implementation. Thus, it has potential applications in biomolecular and biochemical analysis.

中文翻译：

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基于方形晶格光子晶体光纤外部镀金的高灵敏度折射率传感器

提出了一种基于外部金涂层的高灵敏度方格光子晶体光纤 (PCF) 折射率 (RI) 传感器。这种设计消除了微米孔中选择性涂层和液体渗透的限制，避免了D型光纤的侧面抛光。使用全矢量有限元法（FV-FEM）详细研究了气孔直径和金膜厚度对传感性能的影响。此外，将优化参数下镀金PCF的传感性能与具有相同气孔直径和金光栅的PCF的传感性能进行了比较。结果表明，所提出的 PCF 对气孔直径具有更高的结构公差，从而提高了制造可行性。此外，镀金 PCF 的最大灵敏度为 31 000 nm RIU⁻¹和 3.23 × 10 ⁻⁶  RIU分辨率，RI 测量范围为 1.34–1.49。在1.38-1.46的RI检测范围内，具有较低损耗的金光栅PCF的最大灵敏度为30 000 nm RIU ^-1，分辨率为3.33 × 10 ^-6  RIU。低损耗有利于延长光纤的长度，便于实际实施。因此，它在生物分子和生化分析中具有潜在的应用价值。