Wei Zeyong, Li Shuqiao, Xie Lingyun, Deng Xiao, Wang Zhanshan, Cheng Xinbin
Opt Express. 2022 Sep 26;30(20):36863-36872. doi: 10.1364/OE.473192.
Free-space orbital angular momentum (OAM) communication is considered as one of the potential alternative on-chip optical interconnect solutions. The number of OAM modes determines the capacity of high-speed communication. However, existing integrated vortex beam emitters have a constraint relationship between the number of OAM modes and the emitter size, rendering it difficult to emit more OAM modes with a small-sized emitter. In view of the above, this study proposes an on-chip ultracompact multimode vortex beam emitter based on vertical modes, which permits more OAM modes without requiring an increase in the size of the emitter. Vertical modes in large-aspect-ratio waveguides are pointed out to enable multimode microrings with small radii because high-order vertical modes can maintain almost the same horizontal wave vector as that of the fundamental mode. Four-mode and five-mode vortex beam emitters with the same radius of 1.5 µm are designed and the effectiveness of these emitters is verified through simulation. Furthermore, a high-efficiency and low-crosstalk approach for high-order vertical mode coupling by varying the waveguide height is presented. This research not only promotes further integration of on-chip optical interconnection, but also provides a new strategy for optical waveguide mode selection in photonic integrated circuits design.
自由空间轨道角动量（OAM）通信被认为是一种潜在的片上光互连替代解决方案。OAM模式的数量决定了高速通信的容量。然而，现有的集成涡旋光束发射器在OAM模式数量和发射器尺寸之间存在约束关系，使得难以用小尺寸发射器发射更多的OAM模式。鉴于此，本研究提出了一种基于垂直模式的片上超紧凑型多模涡旋光束发射器，它可以在不增加发射器尺寸的情况下实现更多的OAM模式。研究指出，大纵横比波导中的垂直模式能够实现具有小半径的多模微环，因为高阶垂直模式可以保持与基模几乎相同的水平波矢。设计了半径均为1.5 µm的四模和五模涡旋光束发射器，并通过仿真验证了这些发射器的有效性。此外，还提出了一种通过改变波导高度实现高阶垂直模式耦合的高效低串扰方法。本研究不仅推动了片上光互连的进一步集成，也为光子集成电路设计中的光波导模式选择提供了新策略。
