A lossy mode resonance (LMR) based fiber optic refractive index (RI) sensor utilizing a layer of fluorine-doped tin oxide (FTO) over the unclad core of the fiber is theoretically analyzed. To enhance its sensitivity, the thickness of the FTO layer is optimized. For further sensitivity enhancement, an over-layer of two different materials, ${{\rm{TiO}}_2}$ and ${\rm{Hf}}{{\rm{O}}_2}$, is used. The sensitivity of ${\rm{FTO}}/{{\rm{TiO}}_2}$ and ${\rm{FTO}}/{{\rm{HfO}}_2}$ bilayer based LMR sensors increases with the increase in the thickness of the over-layer for a fixed thickness of the bilayer. Further, the sensitivity of the sensor utilizing the ${\rm{FTO}}/{{\rm{HfO}}_2}$ bilayer is found to be more than the sensitivity of the ${\rm{FTO}}/{{\rm{TiO}}_2}$ bilayer sensor. To keep the operating spectral range of the sensor in the visible region, the total thickness of the bilayer is adjusted. It is found that a total bilayer thickness of 30 nm with 90% thickness of ${{\rm{HfO}}_2}$ gives the maximum sensitivity of 4400 nm/RIU for 1.33 RI of the sensing medium, which is more than three times the sensitivity of the FTO coated LMR sensor. The sensitivity of the proposed LMR sensor utilizing the ${\rm{FTO}}/{{\rm{HfO}}_2}$ bilayer is compared with the other LMR sensors reported in the literature, and it is found that the proposed sensor possesses the highest sensitivity. The other advantage of the proposed sensor is that it works in the visible region, which reduces the cost of the sensor.

中文翻译：

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使用FTO / HfO ₂双层的基于有损模式共振的高灵敏度光纤折射率传感器，用于在可见光区域中进行操作

从理论上分析了基于损耗模共振（LMR）的光纤折射率（RI）传感器，该传感器在光纤的未包层纤芯上使用了一层掺杂氟的氧化锡（FTO）。为了提高其灵敏度，优化了FTO层的厚度。为了进一步提高灵敏度，使用了两种不同材料的覆盖层：$ {{\ rm {TiO}} _ 2} $和$ {\ rm {Hf}} {{\ rm {O}} _ 2} $。基于双层的LMR传感器的$ {\ rm {FTO}} / {{\ rm {TiO}} _ 2} $和$ {\ rm {FTO}} / {{\ rm {HfO}} _ 2} $双层LMR传感器的灵敏度随对于双层的固定厚度，覆盖层的厚度增加。此外，利用$ {\ rm {FTO}} / {{\ rm {HfO}} _ 2} $的传感器灵敏度双层传感器的灵敏度高于$ {\ rm {FTO}} / {{\ rm {TiO}} _ 2} $双层传感器的灵敏度。为了将传感器的工作光谱范围保持在可见光范围内，请调整双层的总厚度。发现双层总厚度为30 nm，厚度为$ {{\ rm {HfO}} _ 2} $的90％，对于1.33 RI的感测介质，其最大灵敏度为4400 nm / RIU，是三倍以上倍于FTO涂层LMR传感器的灵敏度。使用$ {\ rm {FTO}} / {{\ rm {HfO}} _ 2} $的LMR传感器的灵敏度将双分子层与文献中报道的其他LMR传感器进行比较，发现所提出的传感器具有最高的灵敏度。所提出的传感器的另一个优点是它在可见光区域工作，这降低了传感器的成本。