Fig. 2

Optical properties of BSW with respect to thicknesses of top/additional layer and effective index. a Evolution of the propagation constant of the BSW mode with respect to the top layer thickness (red) and the additional layer thickness (blue). b Reflection spectrum (green line) of 60 nm additional layer TiO₂ and position in the photonic bandgap (greyed surface). The red spectrum shows the product of the period of multilayer and the absolute values of the imaginary part of the BSW wave vector which is perpendicular to the direction of BSW propagation. The values are lower at the edges of the bandgap. Blue stars correspond to the values of the imaginary part of the BSW wave vector for 60, 30, 15 and 0 nm thicknesses of additional layer of TiO₂ in the direction toward decreasing nsinθ scale respectively