GUIDED MODES IN FIBERS WITH PARABOLIC-INDEX CORE AND HOMOGENEOUS CLADDING

Mode propagation characteristics of parabolic-index fibres with a homogeneous cladding are studied by using vector wave analysis. By investigating the asymptotic behaviour of the eigenvalue equations and the field components at cut-off and far from cut-off, a comprehensive and consistent scheme for the designation of the various modes is established. Strong similarities with step index fibres are found for both the mode designation schemes and the degeneracy properties among the hybrid modes as well as the TE0m and TM0m modes. This suggests that the technique employed in this paper can be applied to other types of graded-index fibres. In addition, numerical results obtained by solving the eigenvalue equations for a wide range of parameters are presented, which verify the theoretical predictions. Comparisons with the infinite-core approximation (ICA) and the field decomposition technique (FDT) are given. It is shown that neither the ICA nor FDT are applicable for modes near cut-off. © 1979 Chapman and Hall Ltd.