We propose and numerically verify a design approach to a grating coupler (GC) for in-plane generation and propagation of quasi-TE vortex modes with azimuthal order ±1 within photonic integrated circuits (PICs). In the considered GC design example, silicon nitride waveguides with silica substrate and cladding are used. The shallowly etched grating is illuminated by the incident optical beam from a standard single-mode fiber. We optimize the GC design parameters to maximize the purity of orbital angular momentum (OAM) mode first for the case of a theoretical ideally fabricated grating, and then consider a more practical case of GC design, when the etching resolution is limited. The numerical modeling results show possibility of the vortex mode generation with >96% purity of the target OAM state ±1 at the wavelength 1550 nm. The proposed design, compatible with the standard nanofabrication process, provides a simple, compact and robust solution for various potential PIC-based applications of OAM beams.

中文翻译：

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用于矩形波导中光学涡旋模式生成的光栅耦合器设计


我们提出并数值验证了一种光栅耦合器 (GC) 的设计方法，用于在光子集成电路 (PIC) 内面内生成和传播方位角阶数 ±1 的准 TE 涡旋模式。在所考虑的 GC 设计示例中，使用了具有二氧化硅衬底和包层的氮化硅波导。浅蚀刻光栅由来自标准单模光纤的入射光束照射。我们首先在理论上理想制造的光栅的情况下优化 GC 设计参数，以最大化轨道角动量 (OAM) 模式的纯度，然后在蚀刻分辨率有限时考虑更实际的 GC 设计情况。数值模拟结果表明，在波长 1550 nm 处，目标 OAM 状态 ±1 的 >96% 纯度可能产生涡旋模式。所提出的设计与标准纳米制造工艺兼容，为 OAM 梁的各种潜在的基于 PIC 的应用提供了简单、紧凑且稳健的解决方案。