We propose a fiber design consisting of ring-shaped erbium-doped core surrounded by circularly arranged holes of varying radius in fused silica glass to amplify higher-order orbital angular momentum (OAM) modes. We numerically demonstrate simultaneous amplification of 20 OAM modes ($l = {5}$, 6, 7, 8, 9) with more than 20 dB gain at 1550 nm wavelength while having differential modal gain of 0.12 dB. We also demonstrate amplification of modes over the C-band with gain excursion of less than 2 dB, differential modal gain of less than 0.2 dB, and noise figure less than 4.2 dB. The proposed erbium-doped fiber amplifier would be useful in high-data-rate space-division multiplexing optical-communication systems.

中文翻译：

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用于放大 20 个 OAM 模式的掺铒圆形光子晶体光纤设计

我们提出了一种光纤设计，它由环形掺铒纤芯组成，周围环绕着不同半径的圆形排列的熔融石英玻璃孔，以放大高阶轨道角动量 (OAM) 模式。我们在数值上展示了 20 个 OAM 模式（$l = {5}$ , 6, 7, 8, 9）的同时放大，在 1550 nm 波长处增益超过 20 dB，同时具有 0.12 dB 的差分模式增益。我们还展示了 C 波段上模式的放大，增益偏移小于 2 dB，差分模式增益小于 0.2 dB，噪声系数小于 4.2 dB。所提出的掺铒光纤放大器可用于高数据速率空分复用光通信系统。