According to the standard diffraction theory, apertures much smaller than the wavelength of electromagnetic waves transmit poorly. But it's observed experimentally that the transmission through arrays of subwavelength metallic structures exhibits peaks at some wavelengths. These properties implies novel applications including
dynamic optical subwavelength filters, optic switches, and subwavelength optical fiber couplers. In this paper, we theoretically investigate the transmission of electromagnetic waves through subwavelength magnetic slit arrays. The calculated results show that the transmission can be enhanced at wavelengths without exciting surface polaritons. This enhancement is attributed to the slit-perpendicular surface current induced by the incident electromagnetic waves. Additionally, the position of the enhanced peaks shifts to longer wavelengths and the strength of the peaks exhibits more complicated properties with increasing the permeability of the magnetic material constructing the gratings.
Electromagnetic(EM) energy can propagate along optical waveguides made by using the dependence of surface plasmon polaritons(SPPs) on nanometer gap width between two parallel metallic plates. Finite-difference timedomain (FDTD) was employed to calculate the propagation constant of this nanoscale metallic waveguide. The agreement between the calculated values and results predicted by the theory of metallic waveguide is quite satisfactory. We then demonstrate a branched structure with right-angle bends and structures that can be used as nanoscale interferometers by using the ideal of nanoscale metallic waveguides. EM energy transfer was simulated in these structures by using FDTD method. The results show that bend and insertion losses both remain at an acceptable level. We also simulated EM energy transfer in nanoscale metallic waveguide arrays. It is found that the energy spreads into two main lobes as the light propagates along the waveguides. The separation angle of the two lobes is determined by the period of the array.