Biswas Palas, Basumallick Nandini, Dasgupta Kamal, Ghosh Ajay, Bandyopadhyay Somnath
Appl Opt. 2016 Jul 1;55(19):5118-26. doi: 10.1364/AO.55.005118.
We have shown that strongly overcoupled resonant modes of long-period fiber gratings (LPFGs) can be used to assess the adulteration of olive oil. In this background, we investigate the response characteristics of strongly overcoupled resonant modes of different orders to a surrounding medium, the refractive index (RI) of which is greater than that of the fiber cladding, and in the range where a precise refractive index measurement is immensely useful for inspecting the quality of olive oils and other edible oils. A theoretical simulation that would help in designing a sensor with suitable sensitivity and range of measurement has been presented in detail and also validated with experimental results. It was interesting to observe that in a high RI surrounding, a lower order overcoupled resonant mode is much more sensitive as compared to a higher-order one having a similar coupling coefficient. A quantitative analysis demonstrates that for a particular LPFG, the sensitivity of a strongly overcoupled LP mode was found to be ∼2000 dB/RIU, while that of the LP mode having similar coupling strength was ∼550 dB/RIU in the surrounding refractive index range from 1.458 to 1.520. The results have been validated experimentally.
我们已经表明，长周期光纤光栅（LPFGs）的强过耦合共振模式可用于评估橄榄油的掺假情况。在此背景下，我们研究了不同阶次的强过耦合共振模式对周围介质的响应特性，该周围介质的折射率（RI）大于光纤包层的折射率，且处于精确折射率测量对检测橄榄油和其他食用油质量极为有用的范围内。详细介绍了有助于设计具有合适灵敏度和测量范围的传感器的理论模拟，并通过实验结果进行了验证。有趣的是，在高折射率周围环境中，与具有相似耦合系数的高阶模式相比，低阶过耦合共振模式更为敏感。定量分析表明，对于特定的LPFG，在周围折射率范围为1.458至1.520时，强过耦合LP模式的灵敏度约为2000 dB/RIU，而具有相似耦合强度的LP模式的灵敏度约为550 dB/RIU。实验验证了这些结果。
