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提出栅格周期、光栅长度、级联间距不同的两个长周期光纤光栅级联(CLPG)模型,采用传输矩阵法和耦合模理论对两个长周期光纤光栅级联的光谱特性进行了研究。理论分析表明,级联间距对CLPG透射谱损耗峰的位置影响很小;在一定波长范围内,对特定结构的CLPG,其数值模拟的透射谱为一条直线,出现“光栅透明”现象;依据建立的理论模型,分析并推导出“光栅透明”条件。在CLPG写制实验中,适当调整光栅周期和光栅长度,使其满足“光栅透明”条件,测量光谱显示CLPG透射率几乎为0 dB,实验证明了“光栅透明”现象的存在。
Two long-period fiber grating cascades (CLPGs) with different grid periods, grating lengths and different cascade spacings are proposed. The spectral characteristics of two long-period fiber gratings cascades are studied by using transfer matrix method and coupled-mode theory. The theoretical analysis shows that the cascade spacing has little effect on the location of the CLPG loss peak. In a certain wavelength range, the numerical simulation transmission spectrum of the CLPG has a straight line with a “grating transparency” phenomenon. According to the established theoretical model, we analyze and derive the “raster transparent” condition. In the CLPG experiment, the grating period and grating length were adjusted properly to meet the condition of “grating transparent ”. The measured spectrum showed that the transmittance of CLPG was almost 0 dB. Experiments proved the existence of “grating transparent ” phenomenon.