基于椭球封闭空气腔的光纤复合法布里-珀罗结构折射率传感特性研究

提出了基于微椭球型空气腔的在线型光纤复合法布里-珀罗干涉结构,并对其折射率传感特性进行了研究.椭球型空气微腔是利用光纤熔接机对实芯光子晶体光纤和单模光纤以特定的熔接参数熔接形成.用高斯光束模型和ABCD法则分析了椭球型空气腔的腔内损耗,建立了电磁场在复合法布里-珀罗干涉结构中传播的物理模型.根据腔长比值的不同,环境折射率对干涉条纹的影响有对比度调制和波长调制,主要研究了一种波长调制型复合法布里-珀罗结构折射率传感器.仿真结果表明该折射率传感器在1—1.6范围内不出现折射率转折点;实验结果表明在1.333—1.466范围内,折射率灵敏度～37.088 nm·RIU-1,分辨率约为2.69×10-5.该光纤复合法布里-珀罗结构干涉条纹对比度高、体积小、成本低,用于折射率测量可靠性高、分辨率高、无折射率拐点、温度串扰小.

Refractive index sensing characteristic of a hybrid-Fabry-Pérot interferometer based on an in-fiber ellipsoidal cavity

A hybrid-Fabry-Perot (F-P) interferometer based on an in-fiber ellipsoidal cavity is presented, and the refractive index sensing properties are studied. The ellipsoidal air-microcavity is formed by splicing together a single-mode fiber and a photonic crystal fiber with special arc-discharge technique. The cavity loss is analyzed by using a Gaussian beam model and the ABCD law, and the physical model of electromagnetic transmission is established. According to the cavity length ratio, there are two kinds of the influences of environment refractive index on interference fringe: contrast modulation and wavelength modulation. A fiber refractive index sensor with an enclosed air cavity based on wavelength demodulation is proposed in this paper. The result of simulation shows that the sensors has no turning point in a range of 1-1.6. A wavelength interrogation technique is used to demodulate refractive-index with high sensitivity (～ 37.088 nm·RIU^-1) and high resolution (～ 2.69× 10^-5) and with low temperature crosstalk. Experimental results are in good agreement with the theoretical ones. The F-P fiber sensor also holds advantages such as compactness, low cost, easy fabrication, high contrast, high resolution, no turning point, and low temperature crosstalk.
Keywords： fiber sensing hybrid Fabry-Perot refractive-index measurement wavelength interrogation