Propagation Losses of Guided Modes in an Optical Graded-Index Slab Waveguide with Metal Cladding

Analytical results for propagation Iosses of guided modes in a graded-index slab waveguide (GISW) with metal cladding are presented. When the permittivity in the guiding layer decreases linearly away from the metal surface, the attenuation constant alpha_G of well-guided modes, TE and TM, is approximately proportional to only the ratio (Delta epsilon_i / epsilon₀) / d_i, where Delta epsilon_i is the increment in the permittivity at the metal surface in the direction of the polarization of optical waves, d_ii is the diffusion depth in this direction, and epsilon₀ is the permittivity of free space.