Surface Plasmons on Waveguides with a Perturbed Refractive Index Profile

Surface Plasmons on Waveguides with a Perturbed Refractive Index Profile 

In the perturbation theory, we assume that the magnetic field vector hy of a surface plasmon supported by a general planar waveguide with and without the refractive index profile perturbation is described by Eq. 18. For the unperturbed and perturbed waveguide with permittivity profiles e(x) and s(x) = s(x) + Ss(x), respectively, this equation can be rewritten as  

For a small permittivity profile perturbation (x) 3C fi(x), we can assume that the modal field remains unchanged hy = hy) and the modal propagation constant is altered only slightly 3C ) ). Then, Eq. 52 can be reduced 

Two main types of refractive index perturbations will be discussed here in detail. The first type is a homogeneous change in the refractive index in the whole superstrate. Fig. 13, (herein referred as to bulk refractive index change), which can be described by a change in the permittivity profile, e(x) s(x), where  

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