Researchers from Peking University and the University of Shanghai for Science and Technology have developed a novel method to generate multiple vortex beams of light simultaneously, potentially benefitting terahertz communication devices. The research, published in the journal Light: Advanced Manufacturing, introduces a new approach using metasurfaces to create “orbital angular momentum (OAM) combs” in the terahertz frequency range.

In essence, OAM combs are sets of vortex beams with varying orbital angular momentum (OAM) modes, arranged with equal intensity and spacing. The OAM beams carry information in a swirling pattern (vortex), and thus offer additional data capacity compared to conventional light beams. The team’s innovation lies in their ability to produce multiple vortex beams simultaneously, effectively creating a “comb” of light via metasurfaces.

A novel metasurface design

The key to this breakthrough lies in the metasurface design, which consists of an array of rectangular silicon pillars. By tuning the dimensions of these pillars along the x and y axes, the researchers were able to manipulate the phase of the transmitted light independently for both horizontally and vertically polarized waves. This control over the phase allowed them to create the desired wavefront that forms the OAM combs on the focal plane.

The researchers demonstrated two types of metasurfaces: one that generates OAM combs with arbitrary mode numbers (lengths) and another that produces combs with arbitrary locations and intervals in the OAM spectrum. As the paper stated, “As a proof of concept, we first design a metasurface to generate a pair of polarization-multiplexed OAM combs with arbitrary mode numbers. Furthermore, another metasurface is proposed to realize a pair of polarization-multiplexed OAM combs with arbitrary locations and intervals in the OAM spectrum.”

Next steps

Going forward, the research could open up possibilities for future communication technologies such as given it demonstrated a novel approach for generating and manipulating terahertz waves using all-silicon metasurfaces. Compared to other OAM generation methods, the proposed metasurface approach offers several advantages, such as improved OAM mode capacity, compactness, cost-effectiveness, and polarization multiplexing capability.

The researchers emphasize the advantages of their approach, stating that the “metasurfaces-based scheme can make the devices more compact, and at least double the theoretical capacity of OAM channels through polarization-multiplexing.” A press release on the development describes the potential of the research to “promote the development of ultra-high-capacity terahertz multi-mode communication technology.”

The researchers envision these metasurfaces being used in communication links for wireless terahertz communication. They highlight the potential for increased channel capacity through the use of multi-mode OAM beams and polarization multiplexing.

Yet the team acknowledges that there is room for improvement in terms of the performance consistency of the generated beams. They plan to focus future research on optimizing the efficiency and control of the vortex combs, as well as exploring the integration of these metasurfaces with other terahertz devices to create more compact and versatile systems.