设计和制作了一种基于单模多模细芯单模光纤马赫曾德尔(Mach-Zehnder)干涉仪结构，可同时测量折射率和温度的传感器。该传感器中，多模光纤和细芯单模熔接点充当光耦合器。导入光纤中传输的光经多模光纤后在细芯光纤的纤芯和包层中激发出纤芯模和包层模，不同模式光在细芯光纤中传输时将产生光程差，再经细芯单模熔接点耦合成为导出光纤的纤芯模而干涉。传感器透射光谱随着环境折射率和温度的变化发生漂移，通过监测不同级次的干涉谷可实现折射率和温度的同时测量。通过对传感器的透射光谱进行傅里叶变换分析可知该透射光谱主要由LP01模和LP16模干涉形成。该传感器透射光谱中1535 nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-55.90 nm/RIU和0.0501 nm/℃(其中RIU为折射率单位)；1545 nm附近干涉谷的折射率和温度响应灵敏度的理论值分别为-56.26 nm/RIU和0.0505 nm/℃。在折射率和温度的变化范围分别为1.3449~1.3972和20 ℃~90 ℃的环境中对传感器的响应特性进行实验研究，结果表明：透射光谱中1535 nm附近干涉谷的折射率和温度响应灵敏度分别为-53.03 nm/RIU和0.0465 nm/℃；1545 nm附近干涉谷的折射率和温度响应灵敏度分别为-54.24 nm/RIU和0.0542 nm/℃。理论分析与实验结果相一致。该传感器在生物医学领域有较好的应用前景。

A fiber-optic Mach-Zehnder interferometer (MZI) based on single-mode -multimode-thin-core-single-mode fiber structure is proposed and demonstrated for measuring refractive index and temperature simultaneously. The multimode fiber (MMF) and the thin core fiber-single mode fiber (TCF-SMF) spliced point serves as mode coupler. When the light is launched into the MMF through the lead-in SMF, at the MMF-TCF spliced point, the core mode and cladding modes are excited and propagate in the core and cladding region of the TCF respectively. The optical path difference can be produced between different modes propagating within the TCF. Then, at the TCF-SMF spliced point, the excited cladding modes coupled back into the core of lead-out SMF interfere with the TCF core mode. When the surrounding refractive index (SRI) and temperature change, the transmission spectrum of the sensor shifts. On this basis, the simultaneous measurement of SRI and temperature can be completed by monitoring the dips with different interference orders. The intermodal interference mainly occurs between the core mode LP01 and the cladding mode LP16 based on a fast Fourier transformation analysis for the transmission spectrum of the sensor. The sensitivities of the sensor response to the change of SRI and temperature are theoretically achieved. The SRI and temperature theoretical sensitivities of the interference dips at 1535 nm and 1545 nm are -55.90 nm/RIU, 0.0501 nm/℃, and -56.26 nm/RIU, 0.0505 nm/℃, respectively, where RIU is refractive index unit. The responses of the sensor are experimentally studied at the SRI range from 1.3449 to 1.3972 and temperature range from 20 ℃ to 90 ℃, and the sensitivities -53.03 nm/RIU, 0.0465 nm/℃ and -54.24 nm/RIU, 0.0542 nm/℃ for the two selected interference orders. The theoretical analysis of the sensor is in good agreement with that obtained in the experiment. This kind of sensor can offer attractive applications in biomedical sensing.