Interactions between Plasmonic Nanoantennas and Vortex Beams.

The orbital angular momentum (OAM) of light offers a new degree of freedom for light-matter interactions, yet how to control such interactions with this physical dimension remains open. Here, by developing a numerical method enabling optical OAM simulations, we provide insights into complex plasmon behaviors with the physical dimension of OAM, and we prove in theory that plasmonic nanostructures can function as efficient antennas to intercept and directionally reradiate the power of OAM beams. The interplay between optical OAM and spin angular momentum (SAM) generates novel particle polarizations and radiations, which were inaccessible before. For arrayed nanoparticles, coherent surface plasmons with specific phase retardations determined by OAM of the beams enable directional power radiations, making a phased array antenna. These findings expand our knowledge of nanoplasmonics in the OAM area and are promising for quantum information processing and dynamic sensing of ultraweak biosignals.

All-optical frequency-dependent magnetic switching in metal-insulator-metal stub structures.

Many attempts to switch magnetization with optical pulses were based on free-space coupling schemes of circularly polarized light pulses, so-called all-optical helicity-dependent magnetic switching; however, waveguide coupling schemes are promising for on-chip all-optical magnetic switching. Metal-insulator-metal (MIM) stub structures provide a promising platform for highly integrated photonic circuits, thanks to their compact size, on-chip compatibility, and ease of fabrication. We found clockwise and counterclockwise ring-like modes in the MIM stub structure, which can act as effective magnetic fields with two opposite directions due to the inverse Faraday effect. Effective magnetic field spectra inside the MIM stub have dual resonant peaks at which the effective magnetic field intensity reaches its extreme values with opposite signs, corresponding to binary magnetic states. Switching between the binary magnetic states can be achieved by altering the optical pump frequency. The all-optical frequency-dependent magnetic switching in the MIM stub may provide a chip-compatible and ultracompact tool for ultrafast switching of magnetic order.

Switchable plasmonic routers controlled by external magnetic fields by using magneto-plasmonic waveguides.

We analytically and numerically investigate magneto-plasmons in metal films surrounded by a ferromagnetic dielectric. In such waveguide using a metal film with a thickness exceeding the Skin depth, an external magnetic field in the transverse direction can induce a significant spatial asymmetry of mode distribution. Superposition of the odd and the even asymmetric modes over a distance leads to a concentration of the energy on one interface which is switched to the other interface by the magnetic field reversal. The requested magnitude of magnetization is exponentially reduced with the increase of the metal film thickness. Based on this phenomenon, we propose a waveguide-integrated magnetically controlled switchable plasmonic routers with 99-%-high contrast within the optical bandwidth of tens of THz. This configuration can also operate as a magneto-plasmonic modulator.