Directional excitation of guidance modes is central to many applications ranging from light harvesting, optical information processing to quantum optical technology. Of paramount interest, especially, the active control of near-field directionality provides a new paradigm for the real-time on-chip manipulation of light. Here, it is found that for a given dipolar source, its near-field directionality can be toggled efficiently via tailoring the polarization of surface waves that are excited, for example, via tuning the chemical potential of graphene in a graphene-metasurface waveguide. This finding enables a feasible scheme for the active near-field directionality. Counterintuitively, it is revealed that this scheme can transform a circular electric/magnetic dipole into a Huygens dipole in the near-field coupling. Moreover, for Janus dipoles, this scheme enables actively flipping their near-field coupling and non-coupling faces.
Bibliographical noteFunding Information:
Y.Z. and X.L. contributed equally to this work. The work was sponsored by NSF/EFRI‐1741660; the National Natural Science Foundation of China (NNSFC) under grants numbers 61625502, 11961141010, and 61975176; the Top‐Notch Young Talents Program of China; the Fundamental Research Funds for the Central Universities; and the Singapore Ministry of Education (grant nos. MOE2018‐T2‐1‐022 (S) and MOE2016‐T3‐1‐006).
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