Fabry–Pérot-like phenomenon in the surface plasmons resonant transmission of metallic gratings with very narrow slits

The general role of the surface plasmons in the transmission of the metallic grating with very narrow slits has been numerically described using the finite difference time domain method. The straightforward evidence of the surface plasmons existing in the sharp transmission peak has been given by the near-field distribution of the electrical field’s normal components. The Fabry–Perot-like behavior has also been found in the transmission of surface plasmons resonant mode versus the grating depth. It is concluded that whether the peak of surface plasmons’ resonant transmission emerge or not is mainly determined by the grating depths. Based on the approximate resonant transmission equation proposed in our work, it is revealed that the different physical mechanisms of two resonant modes root in the difference in the power-coupled processes.