Abstract
The existence of gap states within the first stop band is theoretically investigated for surface-plasmon polaritons propagating along metal surfaces structured with finite arrays of nano-grooves/ridges with imperfections. By means of rigorous calculations of all scattering channels on the basis of the reduced Rayleigh equation, it is shown that a mismatch of the grating period, rather than simple vacant/defect sites, favors the opening of gap states (located at midgap for half-period shifts) as a phase step does in distributed feedback gratings. Quality factors of the resulting surface-plasmon polaritons' resonances are limited by radiative leakage and ohmic losses.
© 2007 Optical Society of America
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