Optical transmission through metallic nanoslit with symmetric or asymmetric surface-relief profile

The enhanced optical transmission through metallic nanoslit with symmetric or asymmetric surface-relief profile is investigated based on rigorous electromagnetic theory by using the boundary integral method (BIM). Metallic nanoslits with different geometrical structure surfaces: asymmetric sinusoid surface-relief profile and symmetric sinusoid surface-relief profiles, are investigated. The transmission spectra are calculated and the corresponding intensity distributions of magnetic fields at the resonant wavelengths are numerically emulated and illuminated. The numerical results show that there are two transmission peaks - attributed to the nanoslit geometrical structure and the metallic material, respectively, and the normalized transmittance through the conventionally rectangular nanoslit will be enhanced largely when its surface profile is replaced by the smoothly surface-relief shape of the metallic nanoslit. It is indicated that anomalously high transmission is quite sensitive to the surface geometrical profile of the nanoslit and the incident direction of the light wave.