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镀膜相移长周期光纤光栅(PS-LPFG)由于其结构及设计的灵活性可以改善光纤光栅的滤波特性。运用传输矩阵法,讨论了在镀膜PS-LPFG中不同位置引入单个相移、多个π相移时传输谱的滤波特性。研究发现,引入单个π相移时,会在谐振波长两侧出现两个新的阻带;引入多个π相移时,两个主阻带峰间隔随相移个数的增多而增大。进一步研究表明,薄膜厚度可以更灵活地调节镀膜PS-LPFG传输谱损耗峰的位置及损耗峰大小。随着薄膜厚度的增加,两损耗峰的位置向短波长方向移动,当薄膜厚度增大到一定值后,损耗峰位置向长波方向发生较大突变,同时损耗峰峰值急剧减小,随后损耗峰又将向短波方向移动且峰值逐渐增大。波长较大的损耗峰变化滞后于波长较小的损耗峰。
Coated Phase Shift Long Period Fiber Gratings (PS-LPFGs) improve the filtering properties of fiber gratings due to their structural and design flexibility. The transmission matrix method is used to discuss the filtering characteristics of the transmission spectrum when a single phase shift and multiple π phase shifts are introduced into the PS-LPFG. It is found that when a single π-phase shift is introduced, two new stop bands appear on both sides of the resonant wavelength. When multiple π-phase shifts are introduced, the interval between the two main stop bands increases with the number of phase shifts. Further studies show that the thickness of the film can more flexibly regulate the location of the loss peak of the transmission spectrum of the PS-LPFG coating and the peak size of the loss. As the film thickness increases, the positions of the two loss peaks move to the short wavelength. When the thickness of the film increases to a certain value, the location of the peak of the loss changes greatly toward the long-wave direction, and the peak of loss decreases sharply. Turn to the shortwave direction and the peak value gradually increases. Wavelength loss of the peak changes lag behind the wavelength of the smaller loss peak.