基于Mach-Zehnder干涉仪原理, 利用光纤错位熔接技术设计并制作了一种单模光纤-多模光纤-单模光纤-错位熔接点-单模光纤结构的液体折射率传感器。传感器中的多模光纤和错位连接部分充当光耦合器; 多模光纤在后面的单模光纤的纤芯和包层中激发出纤芯模和包层模, 不同的模式有不同的模式折射率, 经中间单模光纤传输到错位熔接点处时, 不同模式光之间将产生光程差, 经错位熔接点耦合成为导出光纤的纤芯模从而产生干涉。对该传感器输出的干涉光谱中干涉谷功率随外界溶液折射率变化的规律进行了理论分析和实验研究。结果表明: 溶液折射率变化为1.358 9~1392 2时, 干涉谱中1 530 nm附近的干涉谷光功率与溶液折射率呈单调递增关系, 可用于折射率的测量; 折射率变化为1.372 0~1.392 2时, 传感器响应曲线具有很好的线性度, 线性拟合系数为0.998, 对应的灵敏度为252.06 dB/RIU。该传感器制作简单、结构紧凑、成本低、灵敏度高, 可用于生物医学领域液体折射率的实时测量。

According to the principle of Mach-Zehnder interferometers, an optical in-fiber Mach-Zehnder sensor for Surrounding Refractive Index (SRI) is designed and prepared based on single mode fiber/multimode fiber/single mode fiber/misallied fusion spliced point/single mode fiber structures by misallied fusion spliced technology. The multimode fiber and misallied fusion spliced point in this sensor are served as optical couplers. The light from leading in single mode fiber is coupled into a core mode and cladding modes and propagates in the fiber. Because different modes have different effective refractive indices when the light reaches the misallied fusion spliced point, different modes have different optical path lengths, and the intermodal interference will occur. The dip power of the transmission spectral response to the SRI is theoretically analyzed and experimentally studied. The experimental results show that the dip power at wavelength of 1 530 nm increases monotonically with the SRI in a Refractive Index(RI) range of 1.372 0—1.392 2. Moreover, the response curve of the sensor achieves a good linearity of 0.998 at the RI range of 1.372 0—1.392 2, which is corresponding to a high sensitivity of 252.06 dB/RIU.This compact size, low-cost and highly sensitive SRI sensor is easy to be fabricated, and offers attractive applications in biomedical sensing.