Origin of superenhanced light transmission through two-dimensional subwavelength rectangular hole arrays

Superenhanced light transmission through subwavelength rectangular hole arrays have been reported and some investigations have been made into the physical origin of this phenomenon K.J. Klein Koerkamp et al., Phys. Rev. Lett. 92, 183901 (2004)]. In our current work, by performing FDTD (finite difference in the time domain) numerical simulations, we demonstrate that mechanism that is different from surface plasmon polaritons set up by the periodicity at the in-plane metal surfaces may account for this superenhanced light transmission. We suggest that for arrays of rectangular holes with small enough width in comparison to the wavelength of the incident light, standing electromagnetic fields can be set up inside the cavity by the surface plasmons on the hole walls with its intensity being substantially enhanced inside the cavity. So resonant cavity-enhanced light transmission is predominant and responsible for its superenhanced light transmission. Rectangular holes behave as Fabry-Pérot resonance cavities except that the frequency of their fundamental modes is restricted by their TM cutoff frequency. However we believe that both localized surface plasmon modes and surface plasmon polaritons set up by the periodicity at the in-plane metal surfaces have their shares in extraordinary optical transmission of rectangular hole arrays especially when the width of the rectangular hole is not small enough and the metal film is not thick enough.