(color online) (a) Hybrid effective index as a function of the cylinder radius with different refractive indices n. (b) Propagation length. (c) Expansion coefficient of the cylinder mode. (d) Coupling strengths of the cylinder mode and SPP mode. The changes in the refractive indices are 0.1 and 0.02, and the initial refractive index of the cylinders is 3.5. The refractive index n has four different values, which are 3.4, 3.48, 3.52, and 3.6.