We propose a photonic crystal fiber with a high refractive index ring, which supports up to 180 orbital angular momentum (OAM) modes without any high order radial modes from $1.5\ {\boldsymbol{um}}$ to $1.7\ {\boldsymbol{um}}$ . The finite element method is employed to numerically study the properties of the designed fiber. Further research shows that the refractive index differences of all the eigenmodes are above $2 \times {10^{ - 3}}$ , which indicates that the corresponding eigenmodes can be well-separated and ensures the stable transmission of OAM modes. In addition, it is quite interesting that the high order radial modes are significantly suppressed via increasing the radius of the cladding in the design, while most of the OAM modes are without phase distortion, which is beneficial for the (de)multiplexing of the OAM modes. Particularly, the mode quality of all the eigenmodes is higher than $94.9\% $ and the chromatic dispersion is flat with minimum value of the dispersion variation is 0.36 ps/(km·nm). Moreover, the designed fiber possesses various advantages such as low nonlinear coefficient ( $ < 0.7\ /{{\bf W}}/{{\bf km}}$ ) and confinement loss (on the order between ${10^{ - 12}}\ $ and ${10^{ - 7}}\ {\boldsymbol{dB}}/{\boldsymbol{m}}$ ). The proposed fiber has shown great potential for high capacity OAM mode division multiplexing communications.

中文翻译：

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高模质平坦分布色散支持180°角动量模态的光子晶体光纤的数值研究

我们提出了一种具有高折射率环的光子晶体光纤，该光纤可支持多达180种轨道角动量（OAM）模式，而没有任何高阶径向模 $ 1.5 \ {\ boldsymbol {um}} $ 至 $ 1.7 \ {\ boldsymbol {um}} $ 。采用有限元方法对设计纤维的性能进行数值研究。进一步的研究表明，所有本征模的折射率差都在$ 2 \ times {10 ^ {-3}} $ ，表明相应的本征模式可以很好地分离，并确保OAM模式的稳定传输。另外，非常有趣的是，在设计中通过增加包层的半径可以显着抑制高阶径向模式，而大多数OAM模式没有相位失真，这对于OAM的（解复用）是有益的模式。特别是，所有本征模的模态质量都高于$ 94.9 \％$色散平坦，色散变化的最小值为0.36 ps /（km·nm）。而且，所设计的光纤还具有非线性系数低等优点。 $ <0.7 \ / {{\ bf W}} / {{\ bf km}} $ ）和限制损失（按 $ {10 ^ {-12}} \ $ 和 $ {10 ^ {-7}} \ {\ boldsymbol {dB}} / {\ boldsymbol {m}} $ ）。所提出的光纤在大容量OAM模分复用通信中显示出了巨大的潜力。