Subwavelength optical localization with toroidal excitations in plasmonic and Mie metamaterials.

Since the performance of electronic circuits is becoming rather limited in face of intensively increasing of amount of information and related operations, all‐optical processing offers a promising strategy for future information system. It would benefit a great deal if the all‐optical processing could be implemented within the developed electronic chips of nanoscale structures. In that it is highly desirable to break the diffraction limit of light for achieving effective light manipulations with deep subwavelength structures compatible with the state‐of‐the‐art nanofabrication processes. It is of fundamental importance to get subwavelength optical localization, that is, squeeze light wave into subwavelength space for achieving freely manipulating of light fields. This review summarizes the development in realizing subwavelength optical localization by exciting toroidal mode in photonic metamaterials. The toroidal excitations in plasmonic metamaterials and Mie resonant metamaterials, in 3D structures and planar metamaterials, with single or few layers in spectral regime from microwave to optical frequencies are surveyed. Based on the discussion on the configurations of toroidal excitations, the recent development on toroidal‐related optical scattering control actively manipulates the toroidal excitations, and promising applications are further investigated and highlighted. [ABSTRACT FROM AUTHOR]