基于无芯光纤的多参数测量传感器

Multi-parameter measurement sensor based on no-core fiber

设计并制作了一种基于单模-无芯-单模-无芯-单模光纤结构的马赫-曾德尔传感器,可用来同时测量折射率和温度.该传感器中,两处无芯光纤充当输入、输出耦合器,中间单模光纤作为传感臂.利用有限元仿真和理论分析,确定耦合器和传感臂的最优长度为15 mm.在无芯光纤中激发出的高阶模进入单模光纤的包层传输,由于倏逝场的作用,受到环境折射率和温度的影响.选取透射谱不同干涉级次的波谷作为研究对象,实现了折射率和温度的同步测量.实验结果表明:1545 nm附近干涉谷的折射率和温度灵敏度分别为–153.89 nm/RIU(refractive index unit)和0.166 nm/℃;1570 nm附近干涉谷的折射率和温度灵敏度分别为–202.74 nm/RIU和0.183 nm/℃.该传感器在实现折射率和温度同步测量的同时,仍能保持较高灵敏度,在生物医疗等方面有着较好的应用前景.

Aiming at the phenomenon of single measurement parameters and low sensitivity of most Mach-Zehnder sensors based on fiber core mismatch,in this paper we design and build a Mach-Zehnder sensor based on singlemode-no-core-single-mode-no-core-single-mode fiber structure,which can be used to measure refractive index and temperature simultaneously.In this sensor,two no-core optical fiber serve as input and output couplers,the intermediate single-mode is used as a sensing arm.Using finite element simulation and theoretical analysis,the optimal length of the coupler and the sensing arm are determined to be 15 mm.High-order modes excited by no-core optical fiber propagate through the cladding of single-mode fiber,which is affected by the ambient refractive index and temperature because of the influence of the evanescent filed.Trough of different interference orders of transmission spectrum is selected as a research object to realize the simultaneous measurement of refractive index and temperature by using sensitivity coefficient matrix.After the further Fourier transform of the transmission spectrum,the frequency of the main mode that interferes with the fundamental mode is analyzed from the spectrogram to be 0.00098 nm–1.Because of the influence of temperature on the refractive index of water during temperature sensitivity measurement,temperature sensitivity formula and water temperature coefficient are introduced to perform temperature compensation to eliminate the cross sensitivity.In this paper,the 10 mm and 15 mm sensing arms are selected for refractive index comparison experiment,and the temperature experiment is focused on the sensing arm with an optimal length of 15 mm.The experimental results show that the transmission spectrum is blue-shifted with the increase of refractive index in a refractive index range of 1.333–1.397,and the transmission spectrum is red-shifted with the increase of temperature in a temperature range from 30℃to 70℃.The refractive index and temperature sensitivity of the interference valley near 1545 nm are–153.89 nm/RIU and 0.166 nm/℃,respectively;the refractive index and temperature sensitivity of the interference valley near 1570 nm are–202.74 nm/RIU and 0.183 nm/℃,respectively.The experimental results are consistent with the theoretical analyses.Compared with the sensor of the same type,this sensor can still maintain high sensitivity while achieving simultaneous measurement of refractive index and temperature,and has a simple structure,which has a good application prospect in biomedical and other aspects.