Abstract
The Green’s function formalism [see B. Baumeier et al., J. Opt. A, Pure Appl. Opt. 8, S191 (2006)] for calculating the reflection and transmission of light at etched single-groove gratings on both sides of a thin silver film was extended to study the case with double-groove gratings. A splitting of surface-plasmon-polariton (SPP) modes was found due to electromagnetic (EM) coupling between the two grooves in the complex unit cell of the grating. Spectral features corresponding to the split SPP branches (peaks in the transmissivity) were found in this system. In addition, the calculated full spatial distributions of the total EM field were used to provide intuitive explanations for these observations by indicating the high-surface-field regions, the coupling between the two grooves in the same complex unit cell, and the cross coupling between the two nearby grooves located at the upper and lower surfaces of the metal film. The effects on the transmissivity and reflectivity due to changing the depth ratio, groove separation, and lattice constant were also highlighted. The split antisymmetrical SPP mode due to EM coupling between the two grooves in the same complex unit cell, as well as the cross EM coupling between the two nonaligned grooves at the upper and lower surfaces, were found to be responsible for the large peaks found in the transmissivity.
Published Version
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