级联长周期光栅光谱特性

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。结果表明两者光谱存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。

Spectral Characteristics of the Cascaded Long-Period Gratings

The transmission spectra of cascaded long-period grating (LPG) are analyzed using transfer matrix method. The effects of the length,position and loss coefficient of the fiber that connects the LPGs on the cascaded LPG spectral characteristics are discussed. Through numerical analysis, it is shown that the spectra of cascaded LPG and phase shifted LPG have great consistency when the length of the cascading fiber is small or the cascading position is near the end of the cascaded LPG. If other losses are not considered, the amount of transmission loss keeps constant no matter how the length of the cascading fiber changes. The calculation and analysis results also show that if the loss coefficient of the cascading fiber's cladding mode is large enough, the spectra of cascaded LPG can be dealt as incoherent cascading of two LPG spectra, which provides an efficient way to the optimization and design of LPG gain equalizer.