We present a method for exciting surface plasmon polaritons (SPPs) caused by a magnetic field component perpendicular to the direction of slit. The excitation mechanism is based on the spatially oscillating induced current along the edges of the slit under obliquely incident electromagnetic waves. Our finding distinguishes itself from previous mechanisms based on transverse electric fields and unveils the missing point of the SPP-excitation problem in a nanoslit. The use of a magnetic field for SPP excitation can be highly efficient and even comparable to that with an electric field, so that their composition can lead to selective unidirectional excitation.

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An extended and refined scattering-matrix method is proposed for the efficient full parallel implementation of rigorous coupled-wave analysis of multilayer structures. The total electromagnetic field distribution in the rigorous coupled-wave analysis is represented by the linear combination of the eigenmodes with their own coupling coefficients. In the proposed scheme, a refined recursion relation of the coupling coefficients of the eigenmodes is defined for complete parallel computation of the electromagnetic field distributions within multilayer structures.

We present comprehensive case studies on trapping of light in plasmonic waveguides, including the metal-insulator-metal (MIM) and insulator-metal-insulator (IMI) waveguides. Due to the geometrical symmetry, the guided modes are classified into the anti-symmetric and symmetric modes. For the lossless case, where the relative electric permittivity of metal (epsilon(m)) and dielectric (epsilon(d)) are purely real, we define rho as rho = -epsilon(m)/epsilon(d). It is shown that trapping of light occurs in the following cases: the anti-symmetric mode in the MIM waveguide with 1 < rho < 1.28, the symmetric mode in the MIM waveguide with rho <<1, and the symmetric mode in the IMI waveguide with rho <1 . The physical interpretation reveals that these conditions are closely connected with the field distributions in the core and the cladding. Various mode properties such as the number of supported modes and the core width for the mode cut off are also presented.

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