Micro Structure Fiber Sensor

Following the great inventions of laser and optical fiber in1960-1970s, a brand new science, optical fiber sensing technology, was established. The fundamental of optical fiber sensing as following:the characteristic parameters (phase, wavelength, polarization, intensity et al) of core-guided light would be changed when the fiber affected by external environment (temperature, strain, stress, et al), and the information of the external environment can be obtained by analyzing those characteristic parameters. With the continuous development of optical fiber sensing, various kinds of novel fiber sensors have been successively designed and manufactured. Those fiber sensors have been applied in many fields and solved many problems which beyond the ability of the traditional electronic sensors. By contrast to the electronic sensors, the advantages of fiber sensors are obvious: anti-electromagnetic interference, corrosion resistance, good insulation, high sensitivity, good stability, small in size and light weight. Among those now available fiber sensors, the phase modulation type sensors which based on the interferometric technique have the highest sensitivity, which play an irreplaceable role in precise monitoring field. As a representative of phase modulation type sensors, fiber Fabry-Perot (F-P) sensors having been extensive studied by researchers since it has the unique advantages of simple structure, good stability, ease of install and so on. Nowadays, the development direction of fiber sensors is toward to all fiber structure and microstructure, which is the same with the research direction of this dissertation.The title of this dissertation:Microstructure fiber sensor, which is aim to research and manufacture novel optical fiber sensor head. It is easy to understand that the sensor which worked on reflecting model could have a more small structure, so our concentration are focused on the research of novel fiber F-P sensors. In this study, we used experimental method primarily, supplemented by theory analysis. The innovation of this dissertation as following:(1) We propose a compact F-PI sensor whose cavity is an air bubble at the fiber end. And it is achieved in experiment for the first time by using only a single multimode fiber to the best of our knowledge. The manufacture method has the advantage of low-cost, ease of fabrication, batch production. The sensor we fabricated has the advantage of good mechanical strength, good stability. And the cavity length can be changed by adjusting the intensity of Arc discharge. The theory shows that longer cavity length and thinner cavity wall would lead to higher sensitivity. The sensor we make generally has the longest cavity length of150μm and thinnest cavity wall of5μm.(2) For hydrostatic pressure sensing, the sensitivity of our proposed sensor is about0.1nm/MPa which is30times larger than some kind of FBG sensors. For transverse load sensing, it also shows a good performance with the sensitivity of3.64nm/N. The sensor we fabricated is composed of pure silica material, which ensures it could be worked in high temperature environment (up to1000℃). The sensor has a low temperature sensitivity of1.9pm/℃, which make it unsuitable for temperature sensing application. But in the other hand, this property is a good thing since the temperature-cross sensitivity could be avoided when the sensor used in other field, for example, the temperature-cross sensitivity is only-0.02MPa/℃for hydrostatic pressure sensing application. It is worth mentioning that the sensor can be further processed by Femtosecond laser to get a micro-channel across the air bubble for fluid refractive index sensing.(3) We also proposed another kind of phase modulation type sensors:all-fiber temperature sensor based on few mode fiber and single-mode fiber. The sensor also worked on reflection mode and has a small size. The sensor is composed of pure silica material, thus it can be sustainable in high temperature condition (up to900℃). The temperature sensitivity is about O.lnm/N which is10times larger than FBG sensors.