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利用传输矩阵法分析了级联长周期光栅的光谱特性,讨论了级联处光纤的长度、位置以及包层模损耗系数对级联长周期光栅光谱的影响,并对级联长周期光栅和相移长周期光栅的光谱进行了比较。结果表明两者光谱在级联光纤长度较小或级联位置靠近光栅两端时具有较强的一致性,而在级联处光纤较长并且级联位置在中间时,两者表现出截然不同的光谱特性;在不考虑其他损耗的情况下,如果只改变级联处光纤长度,级联长周期光栅总量守恒;此外,当级联长周期光栅在级联处光纤包层模损耗系数较大时,级联长周期光栅的光谱等效于两个长周期光栅光谱的非相干叠加,从而为长周期光栅增益均衡器的优化设计和制作提供了一个简便有效的方法。
The spectral characteristics of cascaded long-period gratings are analyzed by transmission matrix method. The influence of length and position of cladding fiber and the loss coefficient of cladding mode on the spectra of cascaded long-period gratings is discussed. The spectra of the shifted long-period gratings are compared. The results show that the two spectra have strong consistency when the length of the cascaded fiber is small or the position of the cascade is close to the two ends of the grating. When the fiber in the cascade is long and the cascade is in the middle, the spectra show very different The spectral characteristics of cascaded long-period gratings are conserved only when the fiber length at cascade is changed without considering the other losses. In addition, when the cascaded long-period gratings have a higher loss coefficient in the fiber cladding mode When large, the spectrum of the cascaded long-period grating is equivalent to the non-coherent stacking of the two long-period grating spectra, which provides a simple and effective method for the optimization design and fabrication of the long-period grating gain equalizer.