In this paper, we analyse a novel photonic sensor utilising mode-transition in hexagonal photonic crystal fiber (HPCF) to monitor the ethanol content in an ethanol-gasoline blend. Using the finite-element method, the mode-transition from LP cladding-mode to LP core-mode is accomplished by raising the refractive index (RI) of the analyte layer, which removes the necessity of an additional high RI layer deposition at the fiber surface. We have rigorously optimized the air-filling fraction of the HPCF cladding such that the analyte RI range for the mode-transition would correspond to 0–25% v/v of ethanol in the blend, which is within its commercial range of ethanol-gasoline blend. With increasing analyte RI, we have observed the occurrence of a minimum in the total modal power carried by the sensor. We determine the sensitivity through this modal power variation by dividing it (about the power minimum) into two RI dynamic ranges of 1.400–1.410 (i.e., 25–11% ethanol) and 1.410–1.418 (i.e., 11–0% ethanol), respectively. The maximum calculated sensitivity of the sensor within the linear regime of the modal power variation is 0.46 dBm/% v/v and 0.40 dBm/% v/v, respectively, which are twice as high as the sensitivity offered by the FBG and LPG based sensors over the same dynamical range. In addition to the high sensitivity, the proposed sensor does not require any high-RI layer coating, making its design simpler and easier to implement.

中文翻译：

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利用光子晶体光纤固有模式转换的经济高效的乙醇传感器

在本文中，我们分析了一种新型光子传感器，利用六方光子晶体光纤（HPCF）中的模式转换来监测乙醇-汽油混合物中的乙醇含量。使用有限元方法，通过提高分析物层的折射率 (RI) 来完成从 LP 包层模到 LP 芯模的模式转换，从而无需在光纤上沉积额外的高 RI 层表面。我们严格优化了 HPCF 包层的空气填充分数，以便模式转换的分析物 RI 范围将对应于混合物中 0–25% v/v 的乙醇，这在其乙醇-汽油的商业范围内混合。随着分析物 RI 的增加，我们观察到传感器所承载的总模态功率出现最小值。我们通过将模态功率变化（大约功率最小值）分为两个 RI 动态范围 1.400–1.410（即 25–11% 乙醇）和 1.410–1.418（即 11–0% 乙醇）来确定灵敏度，分别。在模态功率变化的线性范围内，传感器的最大计算灵敏度分别为 0.46 dBm/% v/v 和 0.40 dBm/% v/v，是基于 FBG 和 LPG 的灵敏度的两倍传感器具有相同的动态范围。除了高灵敏度之外，所提出的传感器不需要任何高折射率层涂层，使其设计更简单且更容易实现。