Optical switching realized in three-dimensional unusual surface-plasmon-induced photonic crystals composed of plasma-coated spheres

In this paper, the dispersive properties and switching state of three-dimensional (3D) photonic crystals (PCs) with face-centered-cubic lattices, which are composed of core anisotropic dielectric (tellurium) spheres surrounded by non-magnetized plasma shells inserted in the air, are theoretically investigated in detail based on a modified plane wave expansion method. The equations for calculating the band structures for such 3D PCs are deduced. Our analyses show that the proposed double-shell structures can produce the complete photonic band gaps (PBGs) which can work as the optical switching by manipulating the radius of core dielectric sphere and the plasma frequency. However, the switching state of PCs cannot be tuned by the thickness of the plasma shell and plasma collision frequency as the radius of the core dielectric sphere is certain. Numerical simulations also demonstrate that a flatbands region, and the stop band gaps (SBGs) in the (1 0 0) and (1 1 1) directions which are above the flatbands region can be achieved. The SBGs in the (1 0 0) and (1 1 1) directions can also be tuned by the parameters as mentioned above. There is also a threshold value for the thickness of plasma shell, which makes the band structures of such 3D PCs with double-shell structures to be similar to those obtained from the same PCs containing the pure plasma spheres. In this condition, the dielectric function of inserted core sphere will not affect the band structures. It means that the PBGs can be achieved by replacing the pure plasma spheres with such double-shell structures to make fabrication possible and save the material in the realization. It is also noted that the flatbands region is determined by the existence of surface plasmon modes, and the upper edge of flatbands region does not depend on the topology of lattice. The proposed 3D PCs with double-shell structures offer a novel way to realize the tunable optical switching.