Surface-plasmon coupling in subwavelength periodic structures

摘要

Strong reemission of the surface plasmons through a single subwavelength aperture is mainly caused by in-phase coupling of the surface localized electromagnetic waves to irradiative modes by periodic groove structures. By introducing a linear chirping in the groove period, we enhance the coupling effect for focusing the reemitted light in near-field region. The linear chirping in the groove structures which have monotonically decreasing period, leads to focusing the reemitted light with the length, depth, and width of the focus in order of wavelength. We show numerically that the focusing ability is dramatically affected by amount of the linear chirping, and that efficient relaying of a diverging Gaussian beam to a photonic crystal waveguide can be achieved.