The wavelength division multiplexer realized in three-dimensional unusual surface-plasmon-induced photonic crystals composed of the epsilon-negative materials shells

Abstract

In this paper, the dispersive properties and switching state of three-dimensional (3D) photonic crystals (PCs) with diamond lattices, which are composed of the core isotropic dielectric spheres with surrounded by the epsilon-negative (ENG) materials shells inserted in the isotropic dielectric background (air), are theoretically investigated in detail based on a modified plane wave expansion method. The wavelength division multiplexer can be realized easily by tuning the switching state of such PCs. The equations for computing band structures for such 3D PCs are presented. Our analysis shows that the proposed double-shell structures can obtain the complete photonic band gaps (PBGs) which can be realized optical switching with on or off states by manipulating the radius of core dielectric sphere, the relative dielectric constant of background, the dielectric constant of ENG materials and the electronic plasma frequency, respectively. However, the thickness of the ENG materials shell cannot change the switching state as the radius of core dielectric sphere is certain. Numerical simulations also show that a flatbands region, and the stop band gaps (SBGs) in (1 0 0) and (1 1 1) directions which are above the flatbands region can be achieved. The SBGs in (1 0 0) and (1 1 1) directions can also be tuned by the parameters as mentioned above. There also exists a threshold value for the thickness of ENG material shell, which can make the band structures for the 3D PCs with double-shell structures similar to those obtained from the same structure containing the pure ENG materials spheres. In this case, the dielectric function of inserted core sphere will not affect the band structures. It means that we can achieve the PBGs by replacing the pure ENG materials spheres with such double-shell structures to make fabricate easily and save the material in the realization. It is also noticed that the flatband region is determined by the existence of surface plasmon modes, and the upper edge of flatband region does not depend on the topology of lattice. Such presented 3D PCs with double-shell structures offer a novel way to realize the wavelength division multiplexers.