Shao Min, Qiao Xue-guang, Fu Hai-wei, Li Yan, Yao Ni, Jia Zhen-an
Guang Pu Xue Yu Guang Pu Fen Xi. 2016 Sep;36(9):3008-13.
A fiber humidity sensor based on Fiber-Bragg Grating (FBG) sandwiched in single-mode-multimode fiber core-single mode (SMS) fiber structure is proposed and demonstrated. When the surrounding humidity changes, the central wavelength of FBG remains unchanged for it is insensitive to humidity, while the interference spectrum of SMS fiber structure will shift for it is sensitive to the surrounding humidity. Hence, the shift of the SMS fiber structure interference spectrum with humidity could modulate the FBG core mode. Through measuring the reflected power of the FBG core mode the detection of humidity can be realized. The beam propagation of the SMS fiber structure with different lengths of multimode fiber core (MMFC), diameters of MMFC, and surrounding refractive indices are theoretically simulated with beam propagation method. Theoretical simulation indicates that the output core mode power coefficients shift with surrounding humidity of the SMS fiber structure. Experimental results show that the sensor has a linear response to humidity with enhanced sensitivity of 0.06 dBm·(%RH)-1 in the humidity range of 45%95%RH with length of 35 mm and diameter of 85 μm. The temperature effect of the sensor is also discussed, the temperature sensitivity is 0.008 nm·℃-1 in the temperature range of 2080 ℃ and the measurement error of temperature is 0.047% RH·℃-1. Such cost-effective, high sensitive, and reflective power detection based optical fiber humidity sensor could be used in humidity sensing applications.
提出并演示了一种基于夹在单模-多模光纤芯-单模（SMS）光纤结构中的光纤布拉格光栅（FBG）的光纤湿度传感器。当周围湿度变化时，FBG的中心波长保持不变，因为它对湿度不敏感，而SMS光纤结构的干涉光谱会发生偏移，因为它对周围湿度敏感。因此，SMS光纤结构干涉光谱随湿度的偏移可以调制FBG纤芯模式。通过测量FBG纤芯模式的反射功率，可以实现湿度检测。采用光束传播法对不同多模光纤芯（MMFC）长度、MMFC直径和周围折射率的SMS光纤结构的光束传播进行了理论模拟。理论模拟表明，SMS光纤结构的输出纤芯模式功率系数随周围湿度而变化。实验结果表明，该传感器在45%95%RH的湿度范围内，长度为35mm，直径为85μm时，对湿度具有线性响应，灵敏度提高到0.06dBm·(%RH)-¹。还讨论了传感器的温度效应，在2080℃的温度范围内，温度灵敏度为0.008nm·℃-¹，温度测量误差为0.047%RH·℃-¹。这种具有成本效益、高灵敏度且基于反射功率检测的光纤湿度传感器可用于湿度传感应用。
