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介绍一种小芯径折射率引导型光子晶体光纤(PCF)的拉制方法。制备出的光纤纤芯周围第一层空气孔发生形变,呈柚子形,其芯径为1.7μm,孔间距Λ和空气孔直径d分别为3.4μm和2.8μm。由于光纤结构的特殊性,采用有限元法在200~1600 nm波段对其基模有效折射率、色散系数、有效模场面积以及非线性系数进行了数值模拟计算。经过理论计算,这种光纤在所研究的波段具有极高的非线性系数且表现为反常色散,这些特性十分有利于超连续谱的产生。在测量了光纤的损耗、色散等基本特性后,选取损耗较小且位于光纤反常色散区域,中心波长为800 nm的飞秒激光作为光源,将不同功率的超短激光脉冲耦合入光纤,对这种小芯径折射率引导型光子晶体光纤产生超连续谱的过程进行了测量和分析。
A method of drawing a small core diameter refractive index guided photonic crystal fiber (PCF) is introduced. The first layer of air holes around the prepared optical fiber core is deformed and has a grapefruit shape with a core diameter of 1.7 μm, a hole spacing Λ and an air hole diameter d of 3.4 μm and 2.8 μm, respectively. Due to the particularity of the fiber structure, the effective refractive index, dispersion coefficient, effective mode field area and nonlinear coefficient of the fundamental mode are calculated by finite element method in 200 ~ 1600 nm band. After theoretical calculation, this kind of fiber has extremely high non-linear coefficient and exhibits abnormal dispersion in the wave band studied, and these characteristics are very conducive to the generation of supercontinuum. After measuring the basic characteristics of fiber loss and dispersion, the femtosecond laser with a small loss and located in the fiber anomalous dispersion region with a center wavelength of 800 nm was selected as the light source to couple the ultrashort laser pulses with different powers into the fiber. A kind of small core diameter refractive index guided photonic crystal fiber supercontinuum generation process were measured and analyzed.