  Multiresonant metasurfaces could enable many applications in filtering,
sensing and nonlinear optics. However, developing a metasurface with more than
one high-quality-factor or high-Q resonance at designated resonant wavelengths
is challenging. Here, we experimentally demonstrate a plasmonic metasurface
exhibiting different, narrow surface lattice resonances by exploiting the
polarization degree of freedom where different lattice modes propagate along
different dimensions of the lattice. The surface consists of aluminum
nanostructures in a rectangular periodic lattice. The resulting surface lattice
resonances were measured around 630 nm and 1160 nm with Q-factors of ~50 and
~800, respectively. The latter is a record-high plasmonic Q-factor within the
near-infrared type-II window. Such metasurfaces could benefit applications such
as frequency conversion and all-optical switching.

Optics