Enabling Intelligent Omni-Surfaces in the Polarization Domain: Principles, Implementation and Applications

Research in wireless communications based on reconfigurable intelligent surfaces (RIS) has surged in the communication-theoretic arena. Recently, the RIS concept has moved into the area of so-called simultaneously transmitting and reflecting intelligent omni-surfaces (STAR-IOS, or simply IOS), which extend the RIS functionality by incorporating transmission (in addition to reflection) capabilities. Development of STAR-IOS' full and independent reconfiguration capabilities for both reflected and transmitted waves is crucial. However, such full independent reconfiguration has thus far been hampered by the intimate coupling between the transmission and reflection behavior of IOS elements. To overcome this challenge and realize the full potential of reconfigurable IOS-aided systems, in this article we advocate for the use of the polarization domain in the design and operation of STAR-IOS. Thanks to the polarization-dependent features of IOS elements, fully independent (reconfigurable) transmission and reflection modes can be delivered, thus bringing key performance improvements in, and opportunities for, new communication scenarios.