Modal attenuation in a four-layer metal-clad planar waveguide with a semi-parabolically graded guiding layer — an analytical study

Abstract

A general characteristic equation is derived for a four-layer metal-clad graded-index slab waveguide with a guiding layer having a semi-parabolic refractive index profile. The attenuation parameter for the lowest-order TE and TM modes are computed and the results are presented and compared with those obtained by Al-Bader and Jamid for the three-layer case. We make similar calculations for a waveguide with a step-index guiding layer. The attenuation is found to be less sensitive to a change of the guiding layer width in the case of the four-layered structure with a parabolically graded guiding layer than it is for the corresponding three-layered structure. This situation is reversed in the case of a step-index waveguide. Thus the proposed four-layer planar waveguide shows some polarization discrimination properties which are significantly different from those of the three-layer waveguide.