A fiber refractometer with large dynamic range from 1.316 to 1.61 RIU has been realized using a hybrid configuration of a single-mode fiber (SMF) coupled to a stripped-cladding multimode fiber (MMF) as sensing element. An extended analysis of the diffraction principle of a Gaussian beam is specifically developed for this sensor configuration to determine the injected power density into the MMF which, when subsequently combined with ray optics, analytical wave optics and Fresnel equations, enables the sensor response to be comprehensively estimated. Simulation results have been experimentally corroborated to very high agreement for a 2-cm and a 5-cm decladded section of multimode fiber used as the sensing element. The results show, for the shorter sensor (2 cm), a very high sensitivity of ~ −250 a.u./RIU being achieved in the Zone II operating regime, i.e. for indices between the cladding and core indices together with a resolution of $2.76\times 10^{-{6}}$ RIU being attained. In addition, the developed models have been used to accurately predict the response of sensing elements of various lengths, hence demonstrating the potential capability of this research to be exploited for optimizing bespoke design of fiber refractometers of any arbitrary sensing lengths or dimensions. As an example, we present the design of a refractometer achieving a maximum sensitivity of 300 a.u./RIU with a potential resolution of $2.26\times 10^{-{6}}$ RIU.

中文翻译：

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一种用于大动态范围测量的混合光纤折光仪的分析与设计

使用耦合到剥离包层多模光纤 (MMF) 的混合配置的单模光纤 (SMF) 作为传感元件，实现了具有 1.316 到 1.61 RIU 大动态范围的光纤折射计。专门为此传感器配置开发了对高斯光束衍射原理的扩展分析，以确定注入 MMF 的功率密度，当随后与射线光学、分析波光学和菲涅耳方程结合时，使传感器响应全面估计的。对于用作传感元件的 2 厘米和 5 厘米多模光纤的包层部分，仿真结果已被实验证实具有非常高的一致性。结果显示，对于较短的传感器 (2 cm)，具有 ~ -250 au 的非常高的灵敏度 /RIU 在区域 II 运行机制中实现，即包层和核心指数之间的指数以及达到 $2.76\times 10^{-{6}}$ RIU 的分辨率。此外，开发的模型已用于准确预测各种长度的传感元件的响应，因此证明了这项研究的潜在能力，可用于优化任何任意传感长度或尺寸的光纤折射计的定制设计。例如，我们展示了折光计的设计，其最大灵敏度为 300 au/RIU，潜在分辨率为 $2.26\times 10^{-{6}}$ RIU。开发的模型已用于准确预测各种长度的传感元件的响应，因此证明了这项研究的潜在能力，可用于优化任何任意传感长度或尺寸的光纤折射计的定制设计。例如，我们展示了折光计的设计，其最大灵敏度为 300 au/RIU，潜在分辨率为 $2.26\times 10^{-{6}}$ RIU。开发的模型已用于准确预测各种长度的传感元件的响应，因此证明了这项研究的潜在能力，可用于优化任何任意传感长度或尺寸的光纤折射计的定制设计。例如，我们展示了折光计的设计，其最大灵敏度为 300 au/RIU，潜在分辨率为 $2.26\times 10^{-{6}}$ RIU。