A research team led by Prof. Chen Zhigang and Prof. Xu Jingjun from Nankai University has made an advancement in photonic graphene. They have presented a concept of “optical vortex ladder”(OVL) for stepwise generation of optical vortices through Sisyphus pumping of pseudospin modes in photonic graphene with arbitrary integral orbital angular momentum. Furthermore, the OVLs may open exciting new avenues for application of topological singularities, with the potential to impact the fields of optical communications, quantum information computing and complex structured light control. It has been published in the prestigious international journal Nature Communications under the title “Optical Vortex Ladder via Sisyphus Pumping of Pseudospin”.

Optical vortices, featuring wavefront screw dislocations and phase singularities, have captivated great attention for their potential use in optical manipulation, quantum information processing, and optical communications over the decades. Despite technological advancements in optical vortex generation such as spiral phase plates, liquid crystal devices, metasurfaces and nanophotonics, the complex structural design and susceptibility to fabrication defects set avoidable constraints and limitations in many applications. Topological photonics, on the other hand, has opened a promising avenue for creating robust modes that are immune to disorders and defects.

Illustration of an optical vortex ladder (OVL) and Sisyphus pumping in photonic graphene.

In this research, researchers introduced the concept of “Optical Vortex Ladder”. Instead of relying on traditional Gaussian beam excitation, they achieved a complete transition between two distinct pseudospin states in photonic graphene by exciting the Dirac cone with probe beam shaped by a Bessel envelope. Moreover, by employing a Sisyphus pumping method for the pseudospin modes, they successfully generated optical vortices of multi-step ladders. This approach eliminates the need for precise real-space beam alignment and benefits from topological protection in momentum space, offering a way to overcome the limitations of existing vortex generation methods. The principle can be applied beyond photonic graphene and extended to other Dirac-like systems such as Lieb lattices, superhoneycomb lattices, and borophene photonic lattices. These results may pave the way for further exploration of topological systems for active and tunable generation and manipulation of optical vortices, as well as for the development of innovative technologies in the field of photonics and beyond.

Nankai University serves as the principal institution for this research, with postdoctoral researcher Lei Sihong and Prof. Xia Shiqi contributing as co-first authors. Prof. Chen Zhigang, Prof. Song Daohong from Nankai University, and Prof. Hrvoje Buljan from the University of Zagreb, Croatia, serve as co-corresponding authors. The research also benefited from significant guidance from Prof. Xu Jingjun.

For more details, the published paper is available at:
 https://doi.org/10.1038/s41467-024-52070-6.