A simple method enabling the validation of the mode-selection rules obeyed in a single-helix helical long-period fiber grating (SHLPG) has been demonstrated both theoretically and experimentally, which is realized by investigating and analyzing the circular dichroism (CD) and the polarization dependence loss (PDL) spectra of the utilized SHLPG. It is confirmed for the first time, to the best of our knowledge, that in terms of the SHLPG’s helicity, the core mode ${{\rm HE}_{\textbf{11}}}$ with either the left circular polarization or the right circular polarization will be selectively coupled into the higher HE or the TE/TM mode, respectively. As a result, the SHLPG would exhibit an enhanced CD, as well as an enhanced PDL near the resonant wavelengths of the HE and TE/TM modes, respectively. The results presented in this Letter will be helpful for efficiently designing and producing SHLPG-based circular polarizers and orbital-angular-momentum generators.

中文翻译：

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演示单螺旋螺旋长周期光纤光栅中遵循的模式选择规则

通过研究和分析圆二色性（CD）和圆二色性（CD）可以实现一种简单的方法，该方法能够验证单螺旋螺旋长周期光纤光栅（SHLPG）中遵守的模式选择规则。所利用的SHLPG的偏振相关损耗（PDL）光谱。就我们所知，这是第一次确认，就SHLPG的螺旋度而言，核心模式$ {{\ rm HE} _ {\ textbf {11}}} $具有左圆极化或右圆极化的光分别被选择性地耦合到较高的HE或TE / TM模式。结果，SHLPG将分别在HE模式和TE / TM模式的谐振波长附近表现出增强的CD以及增强的PDL。本信中提出的结果将有助于有效设计和生产基于SHLPG的圆偏振器和轨道角动量发生器。