Optical mode properties for nano-layered aluminum-doped zinc oxide rectangular waveguides at the epsilon-near-zero spectral point

摘要

The optical mode properties of an anisotropic nano-layered aluminum-doped zinc oxide rectangular waveguides at the epsilon-near-zero spectral point are numerically investigated. The finite element method is used for a numerical study of the optical resonance frequencies for a square Al:ZnO/ZnO waveguide (1 μm width/height). Optical permittivity for multilayered Al:ZnO/ZnO is described using an effective medium approximation. Our numerical finite element method calculations predict a significant spectral shift, a modified free spectral range, and an asymmetric electric field distribution for lower order optical modes. Those modes have resonance wavelengths at the epsilon-near-zero point (~ 1800 nm). We show that the resonant frequency for the lower order TE~(11) mode increases dramatically compared to the non-doped zinc-oxide waveguides, while the higher order modes (e.g, TE~(21)) remain almost at the same frequency. This results in less than a 5% difference in resonance frequencies for these two modes for Al:ZnO/ZnO square waveguide.