空芯光子带隙光纤纤芯-包层交界面的设计

利用平面波展开法计算了圆六边形空气孔按三角形排列的光子晶体带隙,基于带隙图设计了移去7根玻璃毛细管形成纤芯、传输波长λ=1.55 μm的空芯光子带隙光纤的结构参量.随后利用全矢量有限元法计算了所设计的在纤芯-包层交界面处引入石英环的光纤,给出了在不同半径情况下沿z轴方向的光强分布、光强等高线分布图和损耗随引入石英环相对厚度的变化曲线.得出了光纤消除表面模、减小损耗的纤芯外半径取值范围为1.55Λ～1.7Λ,石英环的相对厚度取值范围为1.3～1.5或3.4～3.8.通过分析发现石英环的引入既可以抑制表面模也可以激发表面模,抑制还是激发有赖于纤芯外半径和石英环厚度的选择.

Design of Core-Cladding Interface of Hollow-Core Photonic-Bandgap Fibers

The photonic bandgap structure for a photonic crystal with rounded hexagons air hole arranged by triangular lattice was calculated by plane wave method (PWM), and based on the structure diagram, structure parameters of a seven-cell hollow-core photonic bandgap fiber (PBF) was designed to propagate a lightwave with λ=1.55 μm. And then numerical simulation for a hollow-core PBF with a silica ring introduced at the core-cladding interface was done with full-vectorial finite element method (FEM), and the intensity distribution, intensity contour distribution in z axis and a curve of leakage loss as a function of normalized core thickness were presented. The ranges of out core radius and the normalized thickness of a silica ring for the fiber free of surface modes and reducing loss are 1.55Λ～1.7Λ and 1.3～1.5 or 3.4～3.8 respectively. A silica ring can not only create surface modes but also remove surface modes, which depends on choices of the out core radius and a silica ring thickness.