| The microbend sensor based on fibers which possess characteristics of electric insulation, light weight, good flexibility, small volume, resistance to electromagnetic was applied in the aerospace, geophysical and the monitoring buildings and so on with the development of science and technology. The microbend sensor is the type of intensity modulation and the traditional microbend sensor detect indirectly the environmental parameter, such as temperature, stress, flux, velocity and strain by the loss of the intensity of light in the fiber under the condition of bending. However,the theory of loss is complicated to calculate precisely the bending loss, and the spectrograph was used in most microbend sensors is expensive. So searching for a new method which is maturational theory, small error and convenient to detect the microbend will be important significance.A novel microbend sensor method based on intermodal interference in dual-core Polarization Maintaining Photonic Crystal Fiber(PM-PCF) is presented in this paper. Research on the design of microbend sensor was mostly based on theoretical analysis and simulation calculation. And the experiment has been done to test the design. The main contents are as follows:First, Analysis of characteristics of mode for polarization-maintaining fiber by the theory of electromagnetic fields. Studied the intermodal interference between the low order mode of LP01 and LP11 in PCF.Second, using the finite-element method, the intermodal interference characteristics of the range of wavelength under the dual mode working, the area of mode field and the sensitivity of interference for PCF are analyzed.In order to find the proper fiber to the microbend sensor, the elliptical core PMF, two-hole PCF and near-rectangle PCF are simulated, the results show that the two-hole PCF is more suitable for microbend sensor.Third, using the finite-element beam propagation method(FD-BPM), the mode field which including the effective refractive index and the distribution of electric field of two-hole PCF are analyzed, and the mode field under the condition of microbend was calculated. Then, the output light intensity of intermodal interference was calculated. The relationship between normalized interference output intensity and bending radius of two low order polarization modes in dual-core PM-PCF when modulated with bending. Furthermore, the wavelength influence of microbend sensor characteristics is discussed theoretically.Fourth, the experimental system of microbend sensor based on modular interference is set up. The phenomena of modular interference about two-hole PCF are observed. And the relationship between normalized interference output intensity and bending radius was tested. The results are analyzed and discussed for improving in the future. |
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