光纤Bragg光栅滤波响应的轴向分布特性研究

Axial distribution of filtering response of fiber Bragg gratings

为揭示光纤Bragg光栅(FBG)的局部滤波特征,研究和分析了滤波响应沿光栅轴向的空间分布规律。从均匀、切趾和啁啾型等基本光纤Bragg光栅(FBG)类型出发,分析了反射带滤波光场沿轴向的分布规律。结果表明,均匀型FBG中,光场反射多集中在前1/2个光栅长度内,呈现非对称性;切趾型FBG中,光场反射在光栅长度内的均匀性、对称性得到了改善;啁啾型FBG中,不同波长在光栅轴向的不同位置集中被反射,符合啁啾效应。进而研究了折射率调制、光栅长度对反射光场轴向分布的影响。结果表明,折射率调制的增大使得光场反射区域更加向前1/2个光栅长度内集中,而光栅长度增加对光场反射区域的总体影响较小。并分析了取样FBG、等效相移型取样FBG反射光场的轴向分布,其规律能准确揭示取样函数、等效相移对滤波响应的影响。

The axial distribution of filtering response of fiber Bragg grating（FBG） along grating space is investigated,to clarify the local filtering features of FBG.Firstly,as for uniform,apodized and chirped FBGs,their axial distributions of optical field within the refection band are obtained.In uniform FBGs,the optical field is mostly reflected inside the first half length,and the local optical reflection along the whole length is asymmetric.The local optical reflection in apodized FBGs shows a uniform and symmetric distribution.In chirped FBGs,the optical field at different wavelengths is mostly reflected at different positions of grating length,following the chirp effect.The influence of refractive index and grating length on the axial distribution of reflected optical field is then analyzed.The increase of refractive index modulation leads to that the optical reflected field becomes more concentrated to the first half length,while the rise of grating length shows little impact on the local reflection area.In addition,the axial distributions of sampled FBG and sampled FBG with equivalent phase shift are analyzed as well,resulting in the exact influence of sampling function and equivalent phase shift on the axial distribution.