An orbital angular momentum (OAM) dividable on-chip directional coupler design is proposed. To guide OAM modes of topological charge number l = ±1, a waveguide needs to support TE01 and TE10 modes with degeneracy. When a directional coupler is made with such an OAM mode waveguide, it is additionally required to equalize the horizontal-direction coupling strengths of those two OAM constitutive eigenmodes. Base on the coupled mode theory formulation, we have found that this requirement can hardly be satisfied and devised a modified cross-shaped waveguide structure to solve this problem. An example design of OAM mode directional coupler is demonstrated. The coupling length of the designed device is 670 µm, and our numerical simulation showed negligible degradation of OAM mode purity during the operation of complete optical power transfer between two waveguides. To the best of our knowledge, this is the first proposal of the on-chip OAM mode directional coupler. The proposed design approach can be applied to implement various devices for OAM mode-based photonic integrated circuits.

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基于轨道角动量模的光子集成电路的定向耦合器设计

提出了一种可分为片上定向耦合器的轨道角动量（OAM）设计。指导拓扑计费号l的OAM模式=±1，波导需要支持简并的TE01和TE10模式。当用这种OAM模式波导制成定向耦合器时，还需要使这两个OAM本征本征模式的水平方向耦合强度相等。基于耦合模式理论公式，我们发现很难满足这一要求，并设计了一种改进的十字形波导结构来解决该问题。演示了OAM模式定向耦合器的示例设计。设计的器件的耦合长度为670 µm，我们的数值模拟表明，在两个波导之间进行完全光功率传输时，OAM模式纯度的降低可以忽略不计。据我们所知，这是片上OAM模式定向耦合器的第一个建议。