Design And Fabrication Of Special Optical Fiber Structures And Their Sensing Characteristics

Optical fiber sensors have been extensively attracted by the researchers due to their small size,light weight, high sensitivity, compact structure, immunity to electromagnetic noise, capability ofsensing in harsh environment, and they have been successively applied to measure variousparameters such as refractive index, temperature, strain. In recent years, more and more peoplehave an interest in the special optical fiber stucture such as taper stucture, and constuct all kinds offiber interferometric sensors, which based on those structures, to detect the changes of the externalenvironment. In addition, the long periodicity of long-period fiber grating results in light couplingfrom the guided core mode to the same direction-propagating cladding modes, so that the long-period fiber grating has a much higher sensitivity than that of fiber Bragg grating. In this paper, westudied the fiber taper structure, and then studied another fiber sensor consiting of bitaper and long-period fiber grating. These results have important significance for the theoretical and practicalapplication.The main chapters of this paper are as follows: in the first chapter, the background and thesignificance of our study were analyzed. The second chapter describes the basic theory of opticalfiber sensing, which includes that the basic theory of fiber-optic waveguide and the fiber phasemodulation sensing principle. A kind of fabrication device and method which is used to fabricatekinds of fiber taper structures was described in Chapter III. Chapter IV has described thefabrication and refractive index sensing characteristics of the fiber taper structure based on largelateral offset fusion splicing. Here, we have fabricated the taper and core-offset structures by aconventional fusion splicer in the manual mode, and then cascaded them to analyze the workingprocess and refractive index sensing characteristics, which is applied the Mach-Zehnderinterferometer principle. We also have analyzed the reason why the cascaded structures have a highsensitivity in the experiments. The fabrication and temperature sensing characteristics of thecascaded structure based on the bitaper and long-period fiber grating were discussed in Chapter V.Here, we introduced the fabrication methods of a waist-enlarged bitaper and long-period fibergrating, and then cascaded the two structures to analyze the working process and temperaturesensing characteristics, in addition, the temperature sensing characteristics of the cascadedstructures at the different resonance wavelengths were discussed experimentally and theoretically.