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用红外飞秒激光逐点刻写低阶光纤布拉格光栅(FBG),光束精确聚焦到光纤纤芯形成很小的光斑是至关重要的。把光纤看作柱透镜,理论分析和用Zemax软件仿真了单个物镜聚焦和柱透镜-物镜组合聚焦两种情况下光纤纤芯的光斑尺寸。单个物镜聚焦时光纤纤芯的光斑尺寸理论计算为0.67μm×84μm,仿真为2.6μm×76μm;柱透镜-物镜组合聚焦时光纤纤芯的光斑尺寸理论计算为3.76μm×0.67μm,仿真为4.1μm×2.2μm。发现利用柱透镜-物镜组合聚焦在纤芯能得到很小的光斑,光纤轴向尺寸大大缩小,这为制作低阶光纤布拉格光栅提供了可能性和基础。
Using infrared femtosecond laser point-by-point writing of a low order fiber Bragg grating (FBG), it is crucial that the beam be focused precisely on the fiber core to form a small spot. Taking the optical fiber as a cylindrical lens, theoretical analysis and Zemax software were used to simulate the spot size of the optical fiber core in both the single objective lens focusing and the objective lens combination focusing. When the focal length of a single objective lens is set, the spot size of the fiber core is 0.67μm × 84μm and the simulation is 2.6μm × 76μm. The spot size of the fiber core is 3.76μm × 0.67μm and the simulation is 4.1μm × 2.2 μm. It is found that the use of a combination of a cylindrical lens and an objective lens to obtain a small spot on the core can greatly reduce the axial size of the optical fiber, which provides the possibility and foundation for fabricating a low-order fiber Bragg grating.