Toward broadband plasmonics: Tuning dispersion in rhombic plasmonic crystals

The angle-dependent optical properties of rhombic plasmonic crystals are described. We show that by extending the capabilities of soft interference lithography, subwavelength periodic patterns with arbitrary 2D Bravais lattices can be generated. In addition, we demonstrate that by lowering the plasmonic crystal lattice symmetry, degenerate conditions can be lifted and more plasmon bands can be excited within a fixed wavelength range. Degeneracies were also removed by changing the polar and azimuthal angles of excitation and visualized in dispersion diagrams. Anticrossings between different plasmon bands were observed to depend significantly on the local refractive index and the excitation direction.