研究了局部压力条件下光纤光栅偏振相关损耗(PDL)的光谱表征。针对次峰现象，详细研究了压力幅度、受压长度和受压位置对次峰产生条件的影响。采用传输矩阵法进行了数值模拟，理论分析和数值仿真显示，受压长度对次峰随压力变化的幅度和波长位移灵敏度有重要影响。在不同的受力长度下，产生次峰需要的受力幅度不同。该研究对利用PDL次峰进行传感具有很好的理论指导意义。

The spectral characterization of polarization dependent loss (PDL) of locally pressed fiber Bragg grating is analyzed. Aimed at secondary peak phenomenon, the effects of the load magnitude, loaded length and loaded position of the grating on the amplitude and position of the created secondary peak are investigated in detail. The numerical simulation based on the modified transfer matrix method is carried on. The theoretical analysis and numerical simulation demonstrate that the loaded length has significant effect on the amplitude and sensitivity of wavelength shifting as function of loaded amplitude of the secondary peak. The load amplitude of creating secondary peak changes under the different loaded lengths. These studies have a good theoretical guidance meaning for sensing using secondary peak of PDL.