Characterization of Extraordinary Transmission for a Single Subwavelength Slit: A Fabry-Pérot-Like Formula Model

Enhanced optical transmission properties of a single subwavelength slit in a metallic film is theoretically studied by the Fabry-Pérot-like formula. By using the analytical model based on a modal expansion method, reflection coefficient of electric field amplitude of surfaces at two slit ends is thoroughly analyzed and an empirical Fabry-Pérot-like formula is derived. Good agreement between our formula and the experimental data is obtained. It is shown that a simple Fabry-Pérot equivalent formula accounts for extraordinary transmission satisfactorily, explaining all of the details of the observed transmission spectra: it is demonstrated that the spacing of two adjacent resonant peaks in the spectra is linearly proportional to the slit width. Also it shows that the linewidth of these resonances increases with increase of the wavelength and is in linear proportion to the slit width. Our Fabry-Pérot-like model can also easily predict on many features of the extraordinary transmission phenomenon.