As wireless applications continue to evolve, the demand for higher data rates and massive connectivity is pushing today’s multiplexing technologies toward their limits. To further increase communication capacity, researchers are exploring structured electromagnetic (EM) waves as new information carriers. In particular, orbital angular momentum (OAM) offers a theoretically unlimited orthogonal set of modes, opening an additional multiplexing dimension for communications. However, applying OAM systems to practical applications remains challenging: generating many distinct OAM modes often relies on bulky components, along with multiple redundant RF chains and external modulators for multi-channel operation, resulting in high cost, large footprint, and complex architecture.
In a new paper published in Light: Science & Applications , a team of scientists, led by Professor Geng-Bo Wu from the State Key Laboratory of Terahertz and Millimeter Wave, Department of Electrical Engineering, City University of Hong Kong, Hong Kong, China, and co-workers have developed a dual-polarized asynchronous space–time–coding metasurface (DASM) controlling all fundamental properties of vortex EM waves, including phase, amplitude, frequency, polarization and momentum. Different OAM modes exhibit distinct helical phase patterns (i.e., they twist around the beam axis at different rates) and are theoretically orthogonal. By jointly exploiting three physical dimensions: OAM mode, polarization, and frequency, DASM significantly increases the number of parallel transmitted channels.
Moreover, the remaining phase and amplitude control provide another key advantage: DASM can directly encode digital information onto the transmitted channels. The DASM-based transmitter can avoid many traditional, bulky, and power-hungry blocks, such as modulators, mixers, and high-speed digital-to-analog converters. As a result, it significantly reduces hardware complexity, power consumption, and overall system overhead. These scientists summarize the operational principle of their high-dimensional multiplexing transmitter:
“We design a dual-polarized asynchronous space-time-coding metasurface with three functionalities: (1) to generate coaxial vortex electromagnetic waves carrying multiple OAM modes through a single, compact aperture; (2) to directly encode independent data streams into these OAM channels, eliminating bulky external modulators and redundant RF chains; and (3) to realize high-dimensional multiplexing by simultaneously exploiting OAM, polarization, and frequency degrees of freedom, thereby enabling multi-channel, high-capacity wireless communications.”
“The communication capacity of this high-dimensional communication framework can grow explosively as more OAM modes and frequency channels are employed,” they added.
“The presented DASM-based approach can not only boost wireless capacity by enabling high-dimensional multiplexing across OAM, polarization, and frequency within a single metasurface aperture, but also simplify transmitters by directly writing data onto multiple EM channels without bulky external modulators and redundant RF chains. This breakthrough could open new opportunities for compact, software-defined ultra-high-speed links in short-range scenarios, such as wireless power transfer, intra-device communications, and data center interconnections,” the scientists forecast.
High-dimensional multiplexing through vortex electromagnetic wave manipulation by space-time-coding metasurfaces