Study On Photonic Crystal Fiber For Hydrostatic Pressure Sensing

Photonic crystal fibers (PCFs) which are also called microstructured optical fibers have attracted considerable attentions due to their unique properties in dispersion, high birefringence, nonlinearity, large mode area, single-polarization-single-mode and so on. Recently, fiber sensors based on PCFs are widely used due to unique properties of PCFs. The main content of this thesis is to design a PCF for hydrostatic pressure sensing, that is to investigated and analysis the mechanical and optical properties of the PCF in the hydrostatic environment, design a high sensitivity pressure sensor based on a specially designed PCF, propose novel hydrostatic pressure sensing system and test the PCF-based pressure sensor. we investigates the internal stress distribution changes when the hydrostatic pressure applied on the PCF based on a finite element method, which results in the cross section refractive change of the PCF. Then we can achieve the relationship between hydrostatic pressure and optical properties based on the analysis of the mode coupling. Based on the principle of photoelastic effect and finite element method, we design several PCFs for hydrostatic pressure sensing and we also analysis their optical properties and hydraulic pressure sensing characteristics. The framework of the thesis is shown as follows:Firstly, the emergence and classification of the optical fiber and the principle and characteristics of PCFs are introduced. In addition, we also introduce the sensing application of the PCFs.Secondly, the simulation principle and calculation method of the PCFs are introduced. For a full understanding of the pressure sensing based on PCFs, the principles such as photoelastic effect and coupled-mode theory are also introduced.Thirdly, we proposed a novel hydrostatic pressure sensing scheme which can realize hydrostatic pressure sensing based on mode coupling between the two fiber cores of a specially-designed PCF which is a dual-core photonic crystal fiber (DC-PCF).The DC-PCF has two fiber cores. The mode coupling of two fiber cores of the PCF under different hydrostatic pressure is numerically investigated. Our calculations show that the hydrostatic pressure sensitivity of the PCF is3.47pm/MPa.Forthly, in the first part of the4th chapter of our thesis, we proposed another PCF for hydrostatic pressure sensing, which is called side-hole dual-core photonic crystal fiber (SHDC-PCF). The SHDC-PCF has a central part similar to the DC-PCF with the triangular lattice photonic crystal structure, but it has two large air holes in the cross-section outside of the photonic crystal structure region, which essentially provides a built-in transducing mechanism to enhance the pressure-induced index change. A hydrostatic pressure sensor based on a10-cm SHDC-PCF has shown a sensing range from0to500MPa and a sensitivity of32pm/MPa. In the second part of the4th chapter of our thesis, we proposed a third PCF for hydrostatic pressure sensing which is called side-hole two-core photonic crystal fiber (SHTC-PCF). A pressure sensor based on an8-cm SHTC-PCF has a sensitivity of110.8pm/MPa for the measurement range from0Mpa to200Mpa.Fifthly, the conclusion and the prospect of the hydrostatic pressure sensor based on PCFs is presented. We conclude the mainly results and the short comes of our research work and discuss the future work.