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提出一种基于倏逝波吸收原理的分段结构光纤倏逝波传感器。运用光束传播法(BPM)对分段和直形波导模型进行数值模拟,分段波导中高阶模在每次分段的第一个界面上被反复地激发。分析不同结构、纤芯直径和溶液浓度对传感器灵敏度的影响,通过化学腐蚀方法制备出不同结构参数的倏逝波传感器,并用不同浓度亚甲基蓝溶液对传感器的灵敏度特性进行实验验证。实验结果表明,在传感直径相同的条件下,传感长度为5cm分段结构光纤倏逝波传感器的灵敏度为0.0135L/mmol,优于传感长度为6cm的传统的单一直形传感器的灵敏度0.0102L/mmol。分段结构光纤倏逝波传感器能有效地激发光纤中低阶模到高阶模的转变,从而提高传感器的灵敏度。实验结果与模拟和理论结果相符。因此,分段结构光纤倏逝波传感器相对于传统的单一的直形传感器不仅具有较高的灵敏度,且机械强度较高,在物质光谱检测方面有着潜在的应用。
A segmented fiber evanescent wave sensor based on evanescent wave absorption principle is proposed. The beam propagation method (BPM) is used to numerically simulate the segmented and straight waveguide models. In the segmented waveguide, the high order modes are repeatedly excited at the first interface of each section. The influences of different structures, core diameter and solution concentration on the sensitivity of the sensor were analyzed. Evanescent sensors with different structural parameters were prepared by chemical etching method. The sensitivity of the sensor was experimentally verified by different concentrations of methylene blue solution. The experimental results show that the sensitivity of the optical fiber evanescent wave sensor with a sensing length of 5cm is 0.0135L / mmol, which is better than the sensitivity of the conventional single straight sensor with the sensing length of 6cm under the same sensing diameter 0.0102 L / mmol. The segmented optical fiber evanescent wave sensor can effectively stimulate the low-order mode to high-order mode transition in the fiber to improve the sensitivity of the sensor. The experimental results are in agreement with the simulation and theoretical results. Therefore, compared with the traditional single straight sensor, the segmented fiber optical evanescent wave sensor has not only high sensitivity but also high mechanical strength, which has potential applications in spectrum detection of materials.