Opt Lett. 2018 Oct 15;43(20):4935-4938. doi: 10.1364/OL.43.004935.
The transmission characteristics of helically twisted photonic crystal fibers (PCFs) having off-axis cores are theoretically investigated for the first time, to the best of our knowledge. Due to the modified equivalent permittivity and permeability tensors induced by helical twisting, the transmission characteristics of helically twisted PCFs depend on the core position. A beam propagation method developed for helically twisted waveguides, which qualitatively and quantitatively explained the reported transmission spectra of helically twisted PCFs, is used for the analysis. The loss is significantly increased for a shorter wavelength side, if the position of the core is far from the rotation axis, due to the coupling to twist-induced cladding modes. On the other hand, for a longer wavelength side, the loss of one of the components of circularly polarized light is increased; namely, input linearly polarized light becomes close to left- or right-circularly polarized light, depending on the rotation direction. These results indicate that helically twisted PCFs with off-axis cores can be used for core-position-dependent polarization controlling devices.
据我们所知，首次对具有离轴芯的螺旋扭曲光子晶体光纤（PCF）的传输特性进行了理论研究。由于螺旋扭曲引起的等效介电常数和磁导率张量的改变，螺旋扭曲 PCF 的传输特性取决于芯位置。为了分析，我们使用了一种针对螺旋扭曲波导开发的光束传播方法，该方法定性和定量地解释了已报道的螺旋扭曲 PCF 的传输光谱。如果芯的位置远离旋转轴，则由于与螺旋诱导包层模式的耦合，较短波长侧的损耗会显著增加。另一方面，对于较长波长侧，圆偏振光的一个分量的损耗会增加；即，输入的线性偏振光会根据旋转方向接近左或右圆偏振光。这些结果表明，具有离轴芯的螺旋扭曲 PCF 可用于基于芯位置的偏振控制设备。
