Mohammed Nazmi A, El Serafy Hatem O
Appl Opt. 2018 Jan 10;57(2):273-282. doi: 10.1364/AO.57.000273.
This work targets a remarkable quasi-distributed temperature sensor based on an apodized fiber Bragg grating. To achieve this, the mathematical formula for a proposed apodization function is carried out and tested. Then, an optimization parametric process required to achieve the remarkable accuracy that is based on coupled mode theory (CMT) is done. A detailed investigation for the side lobe analysis, which is a primary judgment factor, especially in quasi-distributed configuration, is investigated. A comparison between elite selection of apodization profiles (extracted from related literatures) and the proposed modified-Nuttal profile is carried out covering reflectivity peak, full width half maximum (FWHM), and side lobe analysis. The optimization process concludes that the proposed modified-Nuttal profile with a length (L) of 15 mm and refractive index modulation amplitude (Δn) of 1.4×10 is the optimum choice for single-stage and quasi-distributed temperature sensor networks. At previous values, the proposed profile achieves an acceptable reflectivity peak of 10 dB, acceptable FWHM of 0.0808 nm, lowest side lobe maximum (SL max) of 7.037×10 dB, lowest side lobe average (SL avg) of 3.883×10 dB, and lowest side lobe suppression ratio (SLSR) of 1.875×10 dB. These optimized characteristics lead to an accurate single-stage sensor with a temperature sensitivity of 0.0136 nm/°C. For the quasi-distributed scenario, a noteworthy total isolation of 91 dB is achieved without temperature, and an isolation of 4.83 dB is achieved while applying temperature of 110°C for a five-stage temperature-sensing network. Further investigation is made proving that consistency in choosing the apodization profile in the quasi-distributed network is mandatory. If the consistency condition is violated, the proposed profile still survives with a casualty of side lobe level rise of -73.2070 dB when adding uniform apodization and -46.4823 dB when adding Gaussian apodization to the five-stage modified-Nuttall temperature-sensing network.
这项工作的目标是基于变迹光纤布拉格光栅的一种卓越的准分布式温度传感器。为此，推导并测试了一种提出的变迹函数的数学公式。然后，基于耦合模理论（CMT）完成了实现卓越精度所需的优化参数过程。对旁瓣分析进行了详细研究，旁瓣分析是一个主要判断因素，尤其是在准分布式配置中。对从相关文献中提取的变迹轮廓的精英选择与提出的改进型纳塔尔轮廓进行了比较，涵盖反射率峰值、半高宽（FWHM）和旁瓣分析。优化过程得出结论，长度（L）为15毫米且折射率调制幅度（Δn）为1.4×10的提出的改进型纳塔尔轮廓是单级和准分布式温度传感器网络的最佳选择。在上述值下，提出的轮廓实现了10 dB的可接受反射率峰值、0.0808 nm的可接受半高宽、7.037×10 dB的最低旁瓣最大值（SL max）、3.883×10 dB的最低旁瓣平均值（SL avg）以及1.875×10 dB的最低旁瓣抑制比（SLSR）。这些优化特性造就了一个温度灵敏度为0.0136 nm/°C的精确单级传感器。对于准分布式场景，在无温度情况下实现了91 dB的显著总隔离，对于五级温度传感网络，在施加110°C温度时实现了4.83 dB的隔离。进一步的研究证明，在准分布式网络中选择变迹轮廓时保持一致性是必不可少的。如果违反一致性条件，对于五级改进型纳塔尔温度传感网络，当添加均匀变迹时，提出的轮廓仍能幸存，但旁瓣电平会上升-73.2070 dB，当添加高斯变迹时，旁瓣电平会上升-46.4823 dB。
