空芯光子带隙光纤的损耗特性

Loss characteristic of hollow core photonic bandgap fiber

降低光纤损耗是当前空芯光子带隙光纤的研究重点。以19芯空芯光子带隙光纤为例,采用有限元方法,从光纤结构设计角度出发,系统地研究了光纤结构参数与光纤损耗之间的关联性。研究结果表明,增大包层空气孔层数、包层空气孔占空比以及包层空气孔的倒圆角直径可以有效降低光纤的限制损耗(降低到10-4 dB/km以下);而表面散射损耗的大小取决于芯模和表面模之间的耦合,纤芯壁厚增加以及纤芯扩张系数增大都会导致芯模与表面模的耦合增强,增大光纤表面散射损耗,并且由于表面模的出现也会导致光纤的传输带宽变窄。受光纤结构的限制,19芯空芯光子带隙光纤的光纤损耗难以降到1 dB/km以下,进一步降低光纤损耗,只能通过去掉更多的空气孔,形成更大的空芯结构。研究结果为优化空芯光子带隙光纤结构、降低损耗提供了理论依据和指导。

As the focus of current research on hollow core photonic bandgap fiber,reducing fiber loss is of great importance.In the view of fiber design,taking the 19 cell hollow core photonic bandgap fiber for example,the relationship between structure parameters and loss characteristic was investigated using the finite element method.Simulation results indicate that the confinement loss can be effectively reduced by adjusting the cladding parameters.With the increase of the layer of air holes,the air filling fraction and the fillet diameter at the corners,the confinement loss can be reduced below 10-4 d B/km.While the surface scattering loss,which depends on the coupling between the core mode and the surface mode,increases with the thickness of the core wall as well as the core expansion factor.In addition,the appearance of surface mode also leads to a sacrifice of transmission bandwidth.Limited by the fiber structure,the transmission loss of 19 cell hollow core photonic bandgap fiber is difficult to be reduced to less than 1 d B/km.Further reducing fiber loss can only be achieved by removing more air holes to form a larger hollow core structure.The research achievement provides theoretical basis for the realization of low loss hollow core photonic bandgap fibers.