Tailorable Polarization‐Dependent Directional Coupling of Surface Plasmons

Coupling free-space light into surface plasmons (SPs) has traditionally faced challenges in arbitrarily controlling the directionality of the SPs with respect to the incident polarization. Recently reported polarization-dependent directional coupling of SPs using metasurfaces has attracted enormous attention for its promise in developing innovative and on-demand plasmonic devices. However, further progress has been hampered by the limitation in designating the directional coupling with tailorable polarization-dependent feature and compatible ability to incidence of complex polarization distribution. Here, a directional coupling strategy is introduced to overcome these limits. It is demonstrated that, by utilizing the interference between two pairs of slit resonators with different resonance responses, the directional SP coupling can be expanded to arbitrary group of polarized incidence by simply varying their relative distance, and the SP coupling direction will reverse under the corresponding orthogonally polarized incidence without affecting the efficiency. To exhibit the versatile design capability of the strategy, it is further utilized to construct several polarization-dependent plasmonic devices for controlling SP propagations, including two SP metalenses and a plasmonic Airy beam launcher, in which it is shown that the device can even be designed to work for non-uniformly polarized incidence. The strategy paves a reliable route towards many practical on-chip applications.