Study on the self-collimation phenomena of surface waves in structured metals

Abstract

We demonstrate that surface waves in structured perfect electric conductors can be self-collimated using the finite-difference time-domain method. In this thesis, we consider the perfect electric conductor surface with a square array of square holes. The size of holes($d$) is $0.875a$ and the depth of holes($h$) is $a$. Using the finite-difference time-domain method, the band structure and the equifrequency contour of the surface wave modes are obtained for this structure. From the equifrequency contour the self-collimation frequency($f_p = 0.52 c/a$) is obtained. To demonstrate that the surface wave propagates with no spreading, we calculated the field distributions using the periodic boundary conditions. We found that the surface waves are collimated well in the lateral directions and confined well in the vertical directions. Moreover, we demonstrate the hybrid surface modes which exist in a structured metal surface can be collimated. The size of holes($d$) is $0.6a$ and the depth of holes($h$) is $a$. To model metals, the Drude model is used. The plasma frequency ($\\omega_p$) is $1$, and the damping constant is $0$. We found the self-collimation for this structure occurs for the frequency $f = 0.364c/a$. To analyze the propagation loss, we calculated the Q-factor and the propagation length for various damping constants. It is shown that the structured metal has loss larger than the simple surface plasmon structure.