Dual effective-index method for the analysis of rectangular dielectric waveguides

Two different approximations for the propagation constant of a guided mode in a rectangular dielectric waveguide can be obtained by applying the conventional effective-index method to the waveguide in two different ways. By combining these two approximations with the other two approximations for a complementary mode in a complementary waveguide so that the errors in the approximations can be largely canceled, a more accurate approximation can be derived. Numerical results from analyzing several basic rectangular structures reveal that in most cases the new technique is considerably more accurate than the conventional effective-index method and does not generate ambiguous results as the conventional effective-index method does in the analysis of square dielectric rods.