We have demonstrated an ultra-broadband fiber mode converter based on ${{\rm CO}_2}$-laser inscribed length apodized phase-shifted long-period gratings (LPGs) with a three-section linear length apodization profile, where a $\pi $-phase shift was introduced between two adjacent grating sections. The grating parameters were optimized theoretically to achieve the broadband mode conversion between the ${{\rm LP}_{01}}$ mode and ${{\rm LP}_{11}}$ mode. The demonstrated device provides mode conversion efficiency higher than 90% over an ultra- broad bandwidth of $ {\sim} {182}\;{\rm nm}$. The insertion loss of the LPGs is negligible. Orbital angular momentum modes with left- and right-handed circular polarization can be generated from the demonstrated ultra-broadband mode converter successfully.

中文翻译：

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基于变迹相移长周期光栅的超宽带光纤模式转换器。

我们已经证明了基于超宽带光纤模式转换器$ {{\ RM CO} _2} $ -激光刻切趾长度相移长周期光栅（的LPG）与三段线性长度变迹轮廓，其中$在两个相邻的光栅部分之间引入了相移。理论上优化了光栅参数，以实现$ {{\ rm LP} _ {01}} $模式和$ {{\ rm LP} _ {11}} $模式之间的宽带模式转换。演示的设备在$ {\ sim} {182} \; {\ rm nm} $的超宽带宽上提供了高于90％的模式转换效率。。LPG的插入损耗可以忽略不计。可以从演示的超宽带模式转换器成功生成带有左旋和右旋圆极化的轨道角动量模式。