The correlation between single-slit and inter-slit effects in a subwavelength metal double-slit device

The extraordinary optical transmission (EOT) through a subwavelength metal double-slit structure is calculated to study in detail the correlation between the single-slit and inter-slit effects on the transmissivity. A transmissivity formula is put down which retrieves the numerical results from the finite-difference time-domain simulation method. After some reasonable approximations made, the formula is expressed as the product of two periodic functions, determined by the length of a single slit and inter-slit distance, respectively. This simplified form shows that the interplay between the single-slit and inter-slit effects is almost negligible.