Transmission through a single subwavelength slit surrounded by nonperiodic or approximately periodic grooves in perfect conductive film has been analyzed numerically by the finite-difference time-domain method. Results show that the periodicity of the grooves is not the necessary condition to enhance the transmission, but is sufficient to obtain high enhancement. A spectrum with low enhancement and multiple peaks is obtained through a slit with nonperiodic grooves that is due to the resonances at different wavelengths caused by nonperiodicity. The spectrum of a slit with approximately periodic grooves is almost similar to that of a slit with absolutely periodic grooves regardless of whether the grooves are symmetric with respect to the slit, especially when the deflection of the grooves is very small compared to the grooves’ period.
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