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基于游标效应的高灵敏光纤温度和应变传感器

High-Sensitivity Fiber Optic Temperature and Strain Sensors Based on the Vernier Effect

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摘要

提出一种基于光纤Sagnac干涉仪(FSI)和偏振模干涉仪(PMI)级联结构的高灵敏光纤温度和应变传感器。FSI作为参考干涉仪,是将对温度、应变、弯曲及扭转不敏感的椭圆芯保偏光纤(ECPMF)引入到Sagnac环内制得的。PMI作为传感干涉仪,是对光纤起偏器与末端端面镀金的熊猫型保偏光纤(PMF)的快轴/慢轴以45°角进行熔接制得的。参考干涉仪的自由光谱区(FSR)易被调整为接近传感干涉仪的FSR,从而产生光学游标效应,实现灵敏度放大。实验结果表明:所设计的级联传感器的温度灵敏度达15.56nm/℃,是单个PMI的11.12倍;应变灵敏度达154.04pm/με,是单个PMI的11.81倍。所设计的传感器具有灵敏度高、制作简单、稳定性好等优点,在航空航天、工业生产等领域中具有广阔的应用前景。

Abstract

Objective Optical fiber sensors have been extensively used to measure the external physical properties, such as temperature, refractive index, pressure, and strain, because of their characteristics such as simple structure, compact size, low weight, electromagnetic immunity, and high sensitivity. Generally, the fiber optic temperature and strain sensors are manufactured using fiber Bragg gratings (FBG) and optical fiber interferometers. However, the existing optical fiber sensors cannot meet the requirements in some scenarios that require high measurement sensitivity. Therefore, in this study, we propose using the optical vernier effect to enhance the performances of the optical fiber sensors. Normally, the optical vernier effect is generated by cascading two interferometers, among which one is set as the sensing interferometer and the other is set as the reference interferometer. The current interferometers based on the optical vernier effect generally include two cascading interferometers exhibiting almost identical responses to external disturbance, decreasing the sensitivity of the system. A complex isolation structure is usually applied to the reference interferometer to increase the response difference of the two interferometers with respect to the external disturbance, increasing the complexity of the sensors. Therefore, it is considerably important to design a reference interferometer not sensitive to the changes in external environment and achieve high-sensitivity and high-accuracy sensing of temperature and strain.

Methods In this study, a reference interferometer based on the fiber Sagnac interferometer (FSI) is constructed by introducing an elliptical core polarization-maintaining fiber (ECPMF), which exhibits insensitivity to temperature, strain, bending, and torsion. The cascaded sensor is constructed by cascading a reference interferometer and a sensing interferometer based on polarization-mode interferometers (PMI). The optical vernier effect is obtained by controlling the free spectral range (FSR) of the two interferometers to be close but not equal. Thus, high-sensitivity and high-accuracy temperature and strain sensing is realized. The pigtail of the 3-dB coupler of the reference FSI is cut as short as possible to minimize its response to environmental disturbance. The length, major-axis radius, minor-axis radius, and cladding diameter of ECPMF (IVG PME-1300-125) are 10m, 3μm, 1μm, and 125μm, respectively. The PMI is considered to be the sensing interferometer, which is obtained by splicing a polarizer and a polarization-maintaining fiber (PMF) with the fast/slow axis at of an angle of 45°; the other end of the PMF is gold-coated. The length, core, and cladding diameters of the PMF (YOFC PM1017-A) are 0.94m, 6.5μm, and 125μm, respectively. Furthermore, theoretical analysis, numerical simulation, and experimental verification have been successively conducted based on the above design.

Results and Discussions The output spectra of single FSI, single PMI, and cascaded sensors are analyzed theoretically and simulated to verify that the vernier effect can improve the system sensitivity. Results show that the FSR of PMI and FSI are 2.87 and 3.15nm, respectively. When the birefringence parameter of the PMF is increased from 3.5 × 10 -4to 3.51 × 10 -4, the interference spectrum of single PMI exhibits a 1.12-nm red shift, whereas that of the cascaded sensor exhibits a 12.7-nm red shift. The magnification factor is 11.34. When no strain is applied to the fiber at room temperature, the FSR of PMI, FSI, and cascaded sensors are 2.83, 3.1, and 35nm, respectively. Based on theoretical analysis, the birefringence parameter and beat length of ECPMF are 6 × 10 -5and 25.8mm at 1550 nm, respectively, which are consistent with the product specifications. The magnification factor with respect to the vernier effect obtained via theoretical calculation is 11.48, which is consistent with the simulation results. FSI and FMI are placed on a heating plate with a precision of 0.01 ℃ to investigate the temperature sensing characteristics of FMI and the relative temperature insensitivity of FSI. In the experiment, the temperature measurement ranges from 30 ℃ to 37 ℃ with a step of 1 ℃; each temperature state is maintained for 20min. The temperature sensitivities of dip 1 and 2 are 1.40 and 1.38 nm/℃ for a single PMI, respectively, whereas those of dip 1 and 2 are 168.38 and 157.44 pm/℃ for a single FSI, resulting in a temperature sensitivity that is approximately 1/8 of the single PMI temperature sensitivity. Thus, FSI is insensitive to temperature. After being amplified by the vernier effect, the temperature sensitivity of the cascaded sensors becomes 15.56 nm/℃, which is 11.12 times greater than that of a single PMI and is consistent with the theoretical value of 11.34. FSI and PMI are fixed using an optical adhesive (NORLAND 81) on a microdisplacement platform (Thorlabs, KMTS25E/M) with an accuracy of 1 μm to investigate the strain sensing characteristics of PMI and the relative strain insensitivity of FSI, and the distance between the two platforms is 40cm. Controlled by software, one of the microdisplacement platforms move outward; further, a displacement step of 16μm and a corresponding PMI strain step of 40με are realized, and the strain measurement range is from 0 to 280με. The strain sensitivities of dip 1 and 2 are 13.04 and 12.90pm/με for a single PMI, whereas those of dip 1 and 2 are 2.52 and 2.50pm/με for a single FSI, resulting in a strain sensitivity that is approximately 1/5 of the single PMI strain sensitivity. Thus, FSI is insensitive to strain. After being amplified by the vernier effect, the strain sensitivity of the cascaded sensors becomes 15.56nm/℃, which is 11.81 times greater than that of a single PMI and is consistent with the theoretical value of 11.34. The deviation in values can be attributed to the manual reading of the spectrum.

Conclusions In this study, a highly sensitive optical fiber temperature and strain sensor is proposed by introducing ECPMF into the Sagnac ring as a reference interferometer. The sensor includes a reference interferometer FSI and a sensing interferometer PMI, and the lengths of PMF and ECPMF are reasonably designed to make the FSR of FSI and PMI close but not equal, resulting in a vernier effect. The experimental results show that the temperature and strain sensitivity of the cascaded sensor become 15.56 nm/℃ and 154.04 pm/με, respectively, which are 11.12 and 11.81 times greater than that associated with a single PMI, respectively, and consistent with the simulation results. Thus, the effectiveness and reliability of the proposed scheme are verified based on the experimental results. The obtained sensor exhibits high sensitivity, a simple structure, good stability, and a good application prospect in various fields such as aerospace and industrial production.

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中图分类号:TN929.11

DOI:10.3788/CJL202148.0106004

所属栏目:光纤光学与光通信

基金项目:国家自然科学基金(51627804)、安徽省省级重点研发项目(1804a0802214)、国家重点研发项目(2016YFC0301902)

收稿日期:2020-07-10

修改稿日期:2020-08-21

网络出版日期:2021-01-01

作者单位    点击查看

方莎莎:安徽大学信息材料与智能感知安徽省实验室, 安徽 合肥 230601
吴许强:安徽大学信息材料与智能感知安徽省实验室, 安徽 合肥 230601安徽大学光电信息获取与控制教育部重点实验室, 安徽 合肥 230601
张刚:安徽大学信息材料与智能感知安徽省实验室, 安徽 合肥 230601
时金辉:安徽大学信息材料与智能感知安徽省实验室, 安徽 合肥 230601
左铖:安徽大学光电信息获取与控制教育部重点实验室, 安徽 合肥 230601
张伍军:安徽大学光电信息获取与控制教育部重点实验室, 安徽 合肥 230601
桂磊:安徽大学光电信息获取与控制教育部重点实验室, 安徽 合肥 230601
俞本立:安徽大学信息材料与智能感知安徽省实验室, 安徽 合肥 230601安徽大学光电信息获取与控制教育部重点实验室, 安徽 合肥 230601

联系人作者:吴许强(atlaswoo@126.com)

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引用该论文

Fang Shasha,Wu Xuqiang,Zhang Gang,Shi Jinhui,Zuo Cheng,Zhang Wujun,Gui Lei,Yu Benli. High-Sensitivity Fiber Optic Temperature and Strain Sensors Based on the Vernier Effect[J]. Chinese Journal of Lasers, 2021, 48(1): 0106004

方莎莎,吴许强,张刚,时金辉,左铖,张伍军,桂磊,俞本立. 基于游标效应的高灵敏光纤温度和应变传感器[J]. 中国激光, 2021, 48(1): 0106004

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