面向中红外FBG刻写的相位模板衍射光场分析

摘要

The physical model for the inscription of mid-infrared Fiber Bragg Grating (FBG) is established based on the Finite Element Method (FEM). The diffracted light field by the phase mask is analyzed. Two light sources as the plane wave and spherical wave are adopted in the simulation. When using the plane wave as the incident beam, the variation of the Talbot diffraction pattern is deeply analyzed by changing the incident angle of the plane wave and the groove depth of the phase mask. When using the spherical wave as the incident light, the variation of the diffraction pattern of the phase mask is analyzed by changing the distance between the light source and the phase mask. As a result, when the plane wave is incident in an arbitrary angle, the Talbot diffraction pattern is formed along the same direction as the input. The profile and maximum energy of the Talbot diffraction is changed with the groove depth of the phase mask. With the groove depthincreasing, the maximum diffraction energy increases gradually. However, it begins to decrease after the depth reaches certain value. At the same time, the Talbot image tends to evolve to the uniform fringes. When the spherical wave is incident on the phase mask, the distribution of Talbot diffraction pattern is along the propagation direction of the spherical wave. As the distance between the spherical wave and phase mask is decreased, the maximum diffraction energy is higher. Then it begins to decrease after the distance is smaller than some certain value.%基于有限元算法建立用于刻写中红外光纤布喇格光栅(Fiber Bragg Grating, FBG)的相位模板物理模型，对相位模板的衍射光场进行模拟分析。在模拟过程中，采用平面波和球面波两种不同光源。采用平面波作为入射光时，通过改变平面波的入射角度和相位模板光栅的刻槽深度分析Talbot衍射图样的变化。采用球面波作为入射光时，通过改变光源与相位模板的距离分析衍射图样的变化。结果表明，当平面波以任意角度斜入射时，沿与入射光相同方向形成Talbot衍射图样。当改变相位模板刻槽深度时，Talbot衍射图样的形状和能量分布均发生变化：随着刻槽深度的增加，衍射能量最大值逐渐变大；当刻槽超过一定深度时，能量最大值开始减小，同时Talbot图像向均匀条纹演变。当球面波入射到相位模板时，Talbot 衍射图样沿球面波传播方向分布。随着球面波波源逐渐靠近相位模板，能量最大值逐渐升高；当超过一定距离时，能量最大值开始下降。