Chen Haijin, Hu Xuehao, He Meifan, Ren Pengfei, Zhang Chao, Qu Hang
Research Center for Advanced Optics and Photoelectronics, Department of Physics, College of Science, Shantou University, Shantou 515063, Guangdong, China.
Key Laboratory of Intelligent Manufacturing Technology of MOE, Shantou University, Shantou 515063, Guangdong, China.
Sensors (Basel). 2020 Feb 21;20(4):1191. doi: 10.3390/s20041191.
In this paper, we report a capillary-based Mach-Zehnder (M-Z) interferometer that could be used for precise detection of variations in refractive indices of gaseous samples. The sensing mechanism is quite straightforward. Cladding and core modes of a capillary are simultaneously excited by coupling coherent laser beams to the capillary cladding and core, respectively. An interferogram would be generated as the light transmitted from the core interferes with the light transmitted from the cladding. Variations in the refractive index of the air filling the core lead to variations in the phase difference between the core and cladding modes, thus shifting the interference fringes. Using a photodiode together with a narrow slit, we could interrogate the fringe shifts. The resolution of the sensor was found to be ~5.7 × 10 RIU (refractive index unit), which is comparable to the highest resolution obtained by other interferometric sensors reported in previous studies. Finally, we also analyze the temperature cross sensitivity of the sensor. The main goal of this paper is to demonstrate that the ultra-sensitive sensing of gas refractive index could be realized by simply using a single capillary fiber rather than some complex fiber-optic devices such as photonic crystal fibers or other fiber-optic devices fabricated via tricky fiber processing techniques. This capillary sensor, while featuring an ultrahigh resolution, has many other advantages such as simple structure, ease of fabrication, straightforward sensing principle, and low cost.
在本文中，我们报道了一种基于毛细管的马赫曾德尔（M-Z）干涉仪，它可用于精确检测气态样品折射率的变化。其传感机制非常简单。通过分别将相干激光束耦合到毛细管包层和纤芯，同时激发毛细管的包层模和纤芯模。当从纤芯传输的光与从包层传输的光发生干涉时，会产生干涉图。填充纤芯的空气折射率的变化会导致纤芯模和包层模之间的相位差发生变化，从而使干涉条纹移动。使用光电二极管和窄缝，我们可以检测条纹移动。发现该传感器的分辨率约为5.7×10 -6 RIU（折射率单位），这与先前研究中报道的其他干涉式传感器获得的最高分辨率相当。最后，我们还分析了该传感器的温度交叉敏感性。本文的主要目的是证明，仅使用单根毛细管光纤而非一些复杂的光纤器件，如光子晶体光纤或通过复杂光纤加工技术制造的其他光纤器件，就可以实现对气体折射率的超灵敏传感。这种毛细管传感器虽然具有超高分辨率，但还有许多其他优点，如结构简单、易于制造、传感原理直接且成本低。
