Realistic Design of Large-Hollow-Core Photonic Band-Gap Fibers With Suppressed Higher Order Modes and Surface Modes
Realistic Design of Large-Hollow-Core Photonic Band-Gap Fibers With Suppressed Higher Order Modes and Surface Modes
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DOI：
10.1109/jlt.2007.902749
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发表时间：
2007-09
影响因子：
4.7
通讯作者：
K. Saitoh;N. Florous;T. Murao;M. Koshiba;pdf;Fellow Ieee Masanori Koshiba
中科院分区：
文献类型：
--
作者：
K. Saitoh;N. Florous;T. Murao;M. Koshiba;pdf;Fellow Ieee Masanori Koshiba
本文从理论上描述了现实大空心光子带隙光纤（PBGF）中高阶模（HOM）的有效抑制，并将此类波导用于低损耗数据传输应用和高功率光束传输系统。所提出的设计策略基于具有缺陷外芯模式的中央空芯模式的谐振耦合机制。通过在具有六重对称性的PBGF包层中加入六个7单元空气芯，可以将与中央19单元芯中的HOM相对应的光谐振耦合到外部7单元芯中，从而与基模相比显着增加HOM的泄漏损耗。我们考虑具有圆角的六边形气孔的真实 PBGF 结构，并针对 7 单元和 19 单元核心推导出围绕空心核心的二氧化硅环厚度的无表面模式条件。基于有限元模态求解器的 PBGF 分析可确保对所提出设计的传播特性进行验证。数值结果表明，与基模相比，HOM 的泄漏损耗在 200 nm 波长范围内可以提高至少三个数量级，此外，我们还表明，结合具有优化二氧化硅环厚度的真实空气芯可以消除表面模式，并实现对中心芯的强限制和基模非常低的 eta 因子。
This paper theoretically describes effective suppression of higher order modes (HOMs) in realistic large-hollow-core photonic band-gap fibers (PBGFs) and utilizes the use of this class of waveguides for low-loss data-transmission applications and high-power beam delivery systems. The proposed design strategy is based on the resonant-coupling mechanism of central air-core modes with defected outer core modes. By incorporating six 7-unit-cell air cores in the cladding of the PBGF with sixfold symmetry, it is possible by resonantly coupling the light corresponding to the HOMs in a central 19-unit-cell core into the outer 7-unit-cell core, thus significantly increasing the leakage losses of the HOMs in comparison to those of fundamental mode. We consider a realistic PBGF structure with hexagonal airholes having rounded corners and derive a surface-mode-free condition of a silica-ring thickness surrounding the hollow core for both 7-unit-cell and 19-unit-cell cores. Verification regarding the propagation properties of the proposed design is ensured with a PBGF analysis based on a finite element modal solver. Numerical results show that the leakage losses of the HOMs can be enhanced in a level of at least three orders of magnitude over 200-nm wavelength range in comparison to those of the fundamental mode, while in addition, we show that the incorporation of a realistic air core with optimized silica-ring thickness can eliminate surface modes and achieve strong confinement into the central core and very low eta-factor for the fundamental mode.