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通过理论模拟和实验研究了级联倾斜长周期长纤光栅(CTLPFG)的传输谱特性。基于耦合模理论和传输矩阵法,分析了级联长度、级联位置、级联个数和光栅倾角对级联倾斜长周期光纤光栅传输谱的影响:级联长度和级联位置对CTLPFG和级联长周期光纤光栅(CLPFG)传输谱的影响是一致的;随着光栅倾角的增大,CTLPFG的二阶包层模对应的损耗峰增强,三阶包层模对应的损耗峰变化不明显,且二阶包层模显著强于三阶包层模,二阶模的传输谱对60°以上的光栅倾角的变化很敏感;级联段数的增加可以明显增加通带的宽度,且通带宽度与级联段数呈很好的线性关系(回归系数为0.9988),表明CTLPFG在双峰滤波器中有良好的应用价值。实验上,利用逐点写入法刻制了CTLPFG,通过实验结果和理论模拟结果的比较分析,发现实验和理论结果表现出较好的一致性。
The transmission spectral characteristics of cascaded inclined long-period fiber gratings (CTLPFG) were studied theoretically and experimentally. Based on the coupled-mode theory and transmission matrix method, the effects of cascade length, cascade position, number of cascades and grating tilt on the transmission spectra of cascaded inclined long-period fiber gratings are analyzed. The effects of cascade length and cascaded position on CTLPFG and The influence of the transmission spectrum of the long period fiber grating (CLPFG) is consistent. With the increase of the tilt angle of the grating, the corresponding peak loss of the second order cladding mode of the CTLPFG increases, while the loss peak of the third order cladding mode does not change obviously. And the second-order cladding modes are significantly stronger than the third-order cladding modes. The transmission spectra of the second-order modes are sensitive to the variation of grating inclination above 60 °. The increase of the number of cascades can obviously increase the passband width, And cascade segments showed a good linear relationship (regression coefficient of 0.9988), indicating that CTLPFG in the bimodal filter has a good value. Experimentally, CTLPFG was inscribed by point-by-point method, and the experimental and theoretical results showed good agreement through the comparative analysis of experimental results and theoretical simulation results.