Ultra-low-loss all-fiber mode selective couplers (MSCs) have been designed and fabricated using fused biconical taper technique with precise control on phase matching condition. An LP01 MSC with minimum insertion loss about 0.1 dB is fabricated. It is promising for single-mode excitation in large-mode-area few-mode fibers. The insertion loss of the demonstrated LP11 MSC is 0.3 dB at 1540 nm with mode extinction ratio higher than 28 dB. It has a broad operation wavelength from 1480 nm to 1640 nm with wavelength dependent loss about 0.3 dB. To the best of our knowledge, it shows the lowest loss in the reported broadband LP11 mode converters with high mode purity. The fabrication process is reliable and repeatable with smooth power curves, which is of great importance to the practical fabrication of these components. MIMO-less 2 × 25-Gb/s OOK signal and 2 × 20-Gb/s PAM-4 signal transmission over 15-km few-mode fiber have been demonstrated using the fabricated components. The low loss, large bandwidth and the high fabrication repeatability of the mode selective couplers make them promising for low-cost MIMO-less WDM-MDM transmission.

中文翻译：

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用于无 MIMO 的 MDM 传输的超低损耗宽带全光纤模式选择耦合器

超低损耗全光纤模式选择耦合器 (MSC) 已使用熔融双锥锥形技术设计和制造，并精确控制相位匹配条件。制造了具有约 0.1 dB 最小插入损耗的 LP01 MSC。大模面积少模光纤中的单模激发很有前景。所演示的 LP11 MSC 在 1540 nm 处的插入损耗为 0.3 dB，模式消光比高于 28 dB。它具有从 1480 nm 到 1640 nm 的宽工作波长，波长相关损耗约为 0.3 dB。据我们所知，它在报告的具有高模式纯度的宽带 LP11 模式转换器中显示出最低的损耗。制造过程可靠且可重复，功率曲线平滑，这对这些组件的实际制造非常重要。已经使用制造的组件演示了 15 公里少模光纤上的无 MIMO 2 × 25-Gb/s OOK 信号和 2 × 20-Gb/s PAM-4 信号传输。模式选择耦合器的低损耗、大带宽和高制造可重复性使其有望用于低成本的无 MIMO 的 WDM-MDM 传输。