In-plane waveguide optical orbital angular momentum mode generators using subwavelength metamaterials.

Optical orbital angular momentum (OAM) beams have gained significant attention for their potential to enhance the transmission capacity of optical communication systems, in which OAM generators play a critical role. Traditionally, light fields with OAM are generated in free space, while the generation of in-plane OAM modes on a chip suffers from significant challenges. In this study, we propose in-plane waveguide OAM generators by incorporating subwavelength metamaterials into the waveguide. By resorting to mode conversion and superposition in the modulation structure, high-quality OAM _± 1 and OAM _± 2 mode generators are realized with mode purities of up to 98%. This work provides a potential approach for achieving integrated OAM generators for on-chip optical communication and information processing.