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基于严格的光栅三包层模型及其色散方程,对镀膜长周期光纤光栅的折射率传感特性进行了详细的研究。研究发现,镀膜长周期光纤光栅的谐振波长随环境折射率的变化而变化,而且这种变化有一个跳跃,跳跃后的变化与跳跃前相同:如跳跃前向短波方向漂移,则跳跃后也向短波方向漂移。镀膜后,长周期光纤光栅的折射率探测范围得到拓宽,而且探测的灵敏度比没有镀膜时高一个数量级以上。薄膜厚度越接近最优厚度(OOT),镀膜长周期光纤光栅的灵敏度越高。
Based on the strict grating three-layer model and its dispersion equation, the refractive index sensing characteristics of the coated long-period fiber gratings are studied in detail. It is found that the resonant wavelength of the coated long-period fiber grating changes with the change of the refractive index of the environment, and there is a jump in the change. The change after the jump is the same as that before the jump. For example, Shortwave direction drift. After coating, the detection range of the refractive index of the long-period fiber grating is broadened, and the detection sensitivity is more than an order of magnitude higher than that without the coating. The closer the film thickness is to the optimum thickness (OOT), the higher the sensitivity of the coated long-period fiber gratings.