Fabry-Perot tuning of the band-gap polarity in plasmonic crystals

We report experimental observation of Fabry-Perot resonances and Fabry-Perot-induced band-structure flipping in quasi-one-dimensional plasmonic crystals. Angle-resolved transmission spectra of nanoslit arrays in metal films demonstrate band-gap formation resulting from surface plasmon polariton couplings mediated via nanometer-sized waveguide channels. Tuning the waveguide dielectric function and thickness allows for a pronounced resonant enhancement of the coupling strength and band-gap energy and may even induce changes in sign of the coupling-i.e., an effective band-gap flipping. Our results indicate an interesting route towards band-gap engineering in plasmonic crystals.