Geometric Phase Control of Surface Plasmons by Dipole Sources

Geometric phase metasurfaces, as one of the main branches of meta-optics, have attracted enormous interest in the last two decades. Recently, through rotating a set of subwavelength dipole sources, geometric phase concept has been extended to near-field regime for the control of surface plasmons (SPs). Despite this progress, puzzles and shortcomings still exist: it is curious that geometric phases equal to once and twice the rotation angle of dipole source are both reported for SP controls, and the control strategies examined thus far only work for a single wavelength. Hereby, a rigorous derivation of the SP excitation of dipole sources upon circularly polarized illumination is performed, and the rotation dependence and in-plane coordinate correlation of geometric phase control of SPs is clarified. Moreover, a holographic approach is proposed to implement multiplexed geometric phase control, experimentally demonstrating several metalenses that can couple and steer the incident circular polarizations of four wavelengths and two spin directions to different SP focusing beams. This work will pave an avenue toward the development of integrated and multiplexed SP devices.

Automated summary

Geometric phase metasurfaces, a branch of meta-optics, have gained significant attention in recent years. The concept has been extended to near-field regime for the control of surface plasmons (SPs) by rotating dipole sources. However, there are still puzzles and shortcomings, such as the explanation for the reported geometric phases equal to the rotation angle and twice the rotation angle of the dipole sources for SP controls, and the limited control strategies for a single wavelength. In this study, a rigorous derivation of SP excitation by circularly polarized illumination is performed, clarifying the rotation dependence and coordinate correlation of geometric phase control of SPs. Furthermore, a holographic approach is proposed to implement multiplexed geometric phase control, demonstrating the ability to couple and steer incident circular polarizations of different wavelengths and spin directions to specific SP focusing beams. This work paves the way for integrated and multiplexed SP devices.