Dai Daoxin
Opt Express. 2014 Nov 3;22(22):27524-34. doi: 10.1364/OE.22.027524.
A vertical multimode waveguide enabling micro-bends is proposed for mode-multiplexed optical interconnect links. The multimode waveguide is designed to be singlemode in the lateral direction and support higher-order modes in the vertical direction. The characteristic analysis for an SOI (silicon-on-insulator)-based vertical multimode waveguide with a ~0.3μm × ~1.5μm cross section is given as an example. The theoretical pure bending loss is negligible for all the lowest eight modes when the bending radius is even less than 5μm. When light goes through the structure consisting of a straight section connected with a bent section, it is found that some inter-mode crosstalk is caused by the significant mode hybridization happening in the sharply bent multimode waveguide. For the designed SOI-based vertical multimode waveguide, the inter-mode crosstalk is lower than -20dB even when the bending radius is chosen as small as R = 10μm, which is one order smaller than that for the traditional lateral multimode waveguide (whose minimal bending radius is about 130μm). The inter-mode crosstalk can be even reduced to -30dB when choosing R = 30μm. Such a multimode optical waveguide microbend with low inter-mode crosstalk is promising for realizing compact mode-multiplexing links.
本文提出了一种用于模式复用光互连链路的能够实现微弯曲的垂直多模波导。该多模波导设计为在横向为单模，在垂直方向支持高阶模式。以横截面约为0.3μm×1.5μm的基于绝缘体上硅（SOI）的垂直多模波导为例进行了特性分析。当弯曲半径甚至小于5μm时，理论上所有最低的八个模式的纯弯曲损耗都可以忽略不计。当光通过由直段和弯曲段相连组成的结构时，发现在急剧弯曲的多模波导中发生的显著模式杂化会导致一些模式间串扰。对于所设计的基于SOI的垂直多模波导，即使弯曲半径选择小至R = 10μm，模式间串扰也低于-20dB, 这比传统横向多模波导（其最小弯曲半径约为130μm）小一个数量级。当选择R = 30μm时，模式间串扰甚至可以降低到-30dB。这种具有低模式间串扰的多模光波导微弯曲对于实现紧凑的模式复用链路很有前景。
