Positive-permittivity-metal cladding: its effect on the modes of dielectric optical waveguides.

If the real part epsilon1' of the complex permittivity epsilon(1) = epsilon1' - jepsilon(1)" of the metal cladding of a dielectric optical waveguide is positive, well-guided modes can be supported by the dielectric film even if epsilon(1)' is greater than the permittivity of the dielectric film. The attenuation and phase characteristics and the field distributions of the guided modes are discussed for a number of guiding structures, and it is shown that far from cutoff most of the modes exhibit similar properties to those modes supported by the film when the metal cladding has a negative epsilon(1)'. The low order TM modes exhibit different characteristics due to a coupling between them and the surface wave supported by the metal: dielectric interface. This guide has an additional interesting characteristic in that the phase velocities of the TE(0) and TM(0) modes can be made equal.