Transmissions of Metallic Gratings with Narrow Slots

The coupled-wave method (CWM) has been used for transmission analysis of binary metallic gratings with narrow slots. It is proved that waveguide properties of slot determine the transmission in such gratings. For TE waves at given wavelength a minimum width of slot exists, when a considerable transmission can be achieved. For TM waves such certain minimal width does not exist, thus the considerable transmission factor can be obtained (more than 0.8 for grating with Ag) at subwavelength slot. If TM wavelength is negligible higher than grating's period, a resonance of plasmons can appear on one or two surfaces of grating. Last fact decreases the transmission factor. A spectral dependence of the transmission and the dependence of the transmission on grating's thickness are analogical to characteristics of Fabry-Perot interferometer with absorption