Amplitude and phase modulation with electric quadrupole radiation.

Optical metasurfaces can be used to realize various peculiar optical effects, and their mechanisms of the controlling optical phase can be roughly categorized into three types: resonant phase, geometric phase, and propagation phase, also known as the dynamic phase. Multiple mechanisms can be employed to manipulate the phase and amplitude of one metasurface. Therefore, discovering more profound and diverse methods can provide additional degrees of application freedom. This paper proposes a control principle based on electric multipole expansion. We found that for a unit structure formed by dual-metal bars on a metasurface, the radiation of its dipole is equivalent to the interference results of the dual-metal bars. Moreover, the radiation of the quadrupole enables independent control for amplitude and phase. Therefore, we used quadrupole radiation to manipulate the phase and amplitude of the light and even investigated some simple applications, including the realization of focusing light and anomalous refraction. Such a new mechanism of controlling light, combined with other methods, can provide significant insights into achieving challenging goals, like steganography and multifunctional metasurfaces. [ABSTRACT FROM AUTHOR]