  Functional tunability, environmental adaptability, and easy fabrication are
highly desired properties in metasurfaces. Here we provide a tunable bilayer
metasurface composed of two stacked identical dielectric magnetic mirrors,
which are excited by the dominant electric dipole and other magnetic
multipoles, exhibiting nonlocal electric field enhancement near the interface
and high reflection. Differ from the tunability through the direct
superposition of two structures with different functionalities, we achieve the
reversible conversion between high reflection and high transmission by
manipulating the interlayer coupling near the interface between the two
magnetic mirrors. The magnetic mirror effect boosts the interlayer coupling
when the interlayer spacing is small. Decreasing the interlayer spacing of the
bilayer metasurface leads to stronger interlayer coupling and scattering
suppression of the meta-atom, which results in high transmission. On the
contrary, increasing the spacing leads to weaker interlayer coupling and
scattering enhancement, which results in high reflection. The high transmission
of the bilayer metasurface has good robustness due to that the meta-atom with
interlayer coupling can maintain the scattering suppression against adjacent
meta-atom movement and disordered position perturbation. This work provides a
straightforward method (i.e. stacking magnetic mirrors) to design tunable
metasurface, shed new light on high-performance optical switches applied in
communication and sensing.
