We report on a new type of long-period-grating generated in a helical core fiber by bending. The grating arises from bend-induced modulation of an equivalent refractive index in the helical core with a period equal to the helix pitch. We experimentally demonstrate that such grating induces multiple resonant couplings between the fundamental modes guided in the central core and the helical side-core. We have also shown that by varying a direction of bending, one can generate the phase shifted grating. The experimental results are supported by numerical simulations based on the coupled mode equations.

中文翻译：

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螺旋芯光纤中的弯曲诱导长周期光栅

我们报告了一种通过弯曲在螺旋芯纤维中产生的新型长周期光栅。光栅来自于弯曲诱导的螺旋芯中等效折射率的调制，周期等于螺旋螺距。我们实验证明，这种光栅在中心磁芯和螺旋侧磁芯中引导的基本模式之间引起多重共振耦合。我们还表明，通过改变弯曲方向，可以产生相移光栅。基于耦合模式方程的数值模拟为实验结果提供了支持。