Excitation of multiple surface-plasmon-polariton waves and waveguide modes in a 1D photonic crystal atop a 2D metal grating

The Floquet theory and the transfer-matrix approach were used to investigate the excitation of surfaceplasmon-polariton (SPP) waves and waveguide modes in a structure comprising a one-dimensional photonic crystal (1D PC) of finite thickness on top of a planar thick metallic layer. The solutions of the relevant dispersion equations were used to predict the excitation of multiple SPP waves and waveguide modes when the metallic layer is patterned as a two-dimensional (2D) surface-relief grating. The same structure was experimentally fabricated and optically characterized to validate the theoretical approach. Both the theoretical and experimental results show broadband coupling of incident light of either linear polarization state over a broad range of the angle of incidence. This structure has potential applications in planar optical concentrators.