多方式保偏光子晶体光纤建模仿真及优化

Multi-Mode Bias-Preserving Photonic Crystal Fiber Modelling Simulation and Optimization

摘要: 光子晶体光纤具有大模场面积、高功率载能、高保偏性能等诸多优势。目前性能优良的光子晶体光纤依赖进口且价格昂贵，急需实现国产化。本文按照稳定的正六边形结构排布光子晶体光纤的空气孔，然后分别以对边中线和对角线为对称轴制造空气孔缺陷，得到6种不同结构的几何型保偏光子晶体光纤。经过比较以上6种光纤的双折射大小，得出空气孔缺陷以对角线为轴对称排布的光子晶体光纤具有更佳的保偏性能。之后在光子晶体光纤内部添加一对以对角线为轴对称分布的圆形应力区，使得光纤的双折射达到了10⁻⁴量级。对比最内层无空气孔缺陷的光纤而言，有空气孔缺陷后双折射得到了5 × 10⁻⁶的提升。同时证明了增大应力区面积和减小应力区偏离纤芯距离均对双折射有提升效果。最后分析光纤在不同纤芯折射率和空气孔尺寸下的双折射、限制性损耗和基模有效面积变化。结果表明，增大纤芯折射率和空气孔尺寸会略微减小光纤的双折射，但是基模模场面积得到了极大的优化。本篇文章对几何和应力双折射进行了详细分析和探究，为光子晶体光纤的设计和制备提供了新思路。

Abstract: Photonic crystal fiber has many advantages such as large mode field area, high power carrying capacity, high bias preserving performance and so on. At present, photonic crystal fibers with excellent performance are imported and expensive, and there is an urgent need for localization. In this paper, the air holes of the photonic crystal fiber are arranged according to the stable hexagonal structure, and then the air hole defects are fabricated by taking the middle line of the opposite side and the diagonal line as the symmetry axis respectively, so as to obtain six kinds of geometrically bias-preserving photonic crystal fibers with different structures. After comparing the birefringence sizes of the above six optical fibers, it is concluded that the photonic crystal fiber with the air hole defects arranged symmetrically on the diagonal axis has a better bias preserving performance. Afterwards, a pair of circular stress zones with diagonally symmetric distribution were added inside the photonic crystal fiber, which made the birefringence of the fiber reach the magnitude of 10⁻⁴. In comparison with the fiber without air hole defects in the innermost layer, the birefringence was enhanced by 5 × 10⁻⁶ with air hole defects. It is also demonstrated that both increasing the area of the stress region and decreasing the distance of the stress region away from the core have an enhancing effect on the birefringence. Finally, the changes of birefringence, limiting loss and effective area of fundamental mode are analyzed for fibers with different core refractive indices and air hole sizes. The results show that increasing the core refractive index and air hole size slightly reduces the birefringence of the fiber, but the fundamental mode field area is greatly optimized. In this article, geometrical and stress birefringence is analyzed and investigated in detail, providing new ideas for the design and preparation of photonic crystal fibers.