纤芯失配型光纤传感器折射率敏感特性

Sensing Characteristic of Optical Fiber Refractive Index Sensor Based on Core Diameter Mismatch

根据菲涅耳公式和功率反射系数关系式,分析纤芯失配型光纤传感器折射率传感原理;采用单模/多模光纤制作传感器,研究传感器输出光功率随甘油溶液折射率变化特征,并验证理论计算结果。表明媒质折射率n_2=1.300～1.441时,传感器输出光功率强且几乎不发生变化;n_2=1.441～1.452时,传感器输出光功率呈线性快速下降,其斜率为-155.91;当媒质折射率与单模光纤包层折射率接近时,传感器输出光功率几乎为0。验证实验发现,传感器线性快速下降的折射率范围为1.442～1.454,斜率为-49.67,其输出光功率随甘油溶液折射率变化规律与数值模拟结果基本一致。该传感器具有结构简单、成本低、传感系统全光纤化等特点,能用于有毒有害、易燃易爆等特殊环境下物质折射率的高精度测量。

According to Fresnel formula and power reflectance, the sensing principle of optical fiber refractive index sensor based on core diameter mismatch is analyzed. The sensor consists of a multimode fiber in which a short section of standard single-mode fiber is inserted. To validate the theoretical result, output light power of the sensor is studied by glycerin aquatic solution experiments with different refractive indexes. The results show that output light power of the sensor strongly depends on the refractive index of the external medium. The sensor exhibits output light power with no change in the refractive index range of 1.300～1.441. Output light power drops linearly in the range of 1.441～1.452, with slope of -155.91. As the refractive index of the external medium is close to that of single-mode fiber cladding, the corresponding output light power is almost zero. The glycerin aquatic solution experimental result agrees with the theoretical result, and the refractive index range of linear light power dropping is 1.442～1.454, with slope of -49.67. The method is simple and low-cost. All signals of the sensing system are transmitted by fiber. It can measure refractive index of toxic and hazardous solutions with high resolution, and is suitable for gas concentrations measurement in flammable and explosive, strong electromagnetic interference environments and other particular conditions.