Interference and horizontal Fabry-Perot resonance on extraordinary transmission through a metallic nanoslit surrounded by grooves.

The debate on the underlying physics of the extraordinary optical transmission (EOT) through a metallic nano-slit surrounded with periodic grooves is largely resolved. We clarify that the EOT originates from the interference between the slit modes excited by the incident light and by the groove-generated surface plasmon polaritons modulated by the horizontal Fabry-Perot resonance effect due to the surrounding grooves. The quantitative model derived will greatly simplify the design of such structures.