基于莫尔效应的光纤光栅变迹的研究

Apodization of Fiber Bragg Grating Based on Moiré Effect

从理论上分析了利用莫尔效应进行变迹所引起的光纤光栅反射谱和色散特性的变化 ,指出由于莫尔条纹状的折射率调制使平均有效折射率在光栅区维持不变 ,所以可以实现纯变迹。与此成为对照的是 ,常用的升余弦函数变迹由于存在F P腔效应 ,因此在短波边的边模抑制效果不够满意。利用拉伸和二次曝光法产生的莫尔效应 ,实现了对光纤光栅的纯变迹 ,边模抑制比比相同工艺条件下的未变迹提高了约 6dB。

The changes of reflection spectrum and dispersion of fiber Bragg grating (FBG) apodized by moiré effect are analyzed theoretically. It is pointed that the apodization of the fiber grating by using Moiré effect is a pure apodization because the Moiré effect makes the index modulation amplitude in both positive and negative sides and keeps the average index unchanged. However, there exist some side lobes in short wavelength side of Bragg peak when the fiber Bragg grating was apodized by conventional raise cosine function because of the F-P effect. Experimentally apodized FBG by using Moiré effect was obtained with a side mode suppression 6 dB better than conventional FBG without apodization.