Working mechanism of the additional phase operating in the circular co-polarized mode has been revealed

Recently, Professor Zhang Kuang’s research team from our school has made significant progress in the study of phase modulation of metasurfaces. Breaking through the physical bottleneck that traditional geometric phases only act on cross-polarized modes, the team revealed the working mechanism of the additional phase operating in the circular co-polarized mode. Relevant research results were published in Nature Communications under the title Exploiting hidden singularity on the surface of the Poincaré sphere. This study provides a new strategy for wavefront multiplexing of circularly polarized electromagnetic waves while maintaining their polarization state, and holds broad application prospects in fields such as multi-polarization satellite communications and spin-orbit interactions.

Circularly polarized electromagnetic waves are widely used in cutting-edge fields such as satellite communications and quantum optics due to their propagation stability (strong anti-interference ability, stable phase) and the unique property of carrying spin-orbit angular momentum. In the microwave band, the most mature and direct application method is the co-polarized transmission and reception of circular polarization. However, no method for phase adjustment of co-polarized channels has been reported so far.

To break through the existing technical bottlenecks, the team first proposed that the spin-dependent phase mechanism of circularly polarized waves originates from a singularity on the Poincaré sphere, namely the co-polarized singular phase. By optimizing the eigenparameters of the unit to circulate around the singularity along the path with the maximum amplitude, topologically stable 2π phase coverage is achieved under the premise of high efficiency. The team further combined dynamic phases to successfully realize efficient wavefront multiplexing for circular co-polarized channels. This singular phase mechanism provides a universal theory for metasurface phase regulation and wavefront manipulation, and opens up a new model for spin photonics research.

Amplitude-Phase Distribution of Co-polarized Transmission Coefficients in Parameter Space and on the Poincaré Sphere

Experimental Verification of Multiplexing for Left- and Right-Handed Circular Co-polarized Channels