Mode multiplexers are essential components in space/mode division multiplexing. A thermally expanded two-core-fiber-based mode multiplexer/demultiplexer design is proposed, which multiplexes the ${\rm LP}_{01} $ and $ {\rm LP}_{11} $ modes of a two-mode fiber. The extinction ratio of the proposed mode multiplexer is higher than 30 dB over the entire C-band. We extend this design to a three-core-fiber structure that can multiplex/demultiplex both $ {\rm LP}_{11a} $ and $ {\rm LP}_{11b} $ spatial modes. The extinction ratio of the three-core device is found to be more than 23 dB. The same device can work as a $ {\rm LP}_{11} $ filter and $ {\rm LP}_{11} $ tap coupler easily by changing either the core expansion or the scan length.

中文翻译：

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热扩展的基于多芯光纤的模式多路复用器/多路解复用器

模式多路复用器是空/模式划分多路复用中必不可少的组成部分。提出了一种基于热扩展的基于两芯光纤的模式多路复用器/多路分解器设计，该设计多路复用两模式的$ {\ rm LP} _ {01} $和$ {\ rm LP} _ {11} $模式纤维。所提出的模式多路复用器的消光比在整个C波段都高于30 dB。我们将此设计扩展到三芯光纤结构，该结构可以对$ {\ rm LP} _ {11a} $和$ {\ rm LP} _ {11b} $空间模式进行复用/解复用。发现三芯设备的消光比大于23 dB。同一台设备可以用作$ {\ rm LP} _ {11} $过滤器和$ {\ rm LP} _ {11} $ 通过更改核心扩展或扫描长度，可轻松实现抽头耦合器。