Fabry-Perot resonance in slit and grooves to enhance the transmission through a single subwavelength slit

The enhanced transmission through a single subwavelength slit surrounded with periodic grooves has been simulated by a numerical finite-difference time-domain method. We simulated the transmission as functions of slit depth (film thickness) and groove depth, and also the field distributions in the slit and grooves. The transmission varies periodically as functions of slit depth or groove depth, just like the field distribution in the slit or in the groove. These results imply that the resonance mechanisms in the slit and the grooves are the same and we employ a Fabry-Perot like resonance effect to explain it.