Eigenvalue equations for rigorous HE1n and scalar LP0n modes of a step-index fibre are solved numerically above and below the cutoff frequency with account of material losses in the fibre cladding. Polarisation corrections to transverse wavenumbers of the LP02 mode are calculated. Behaviour of dispersion curves in a complex plane of transverse wavenumber in cladding is taken as a basis of the analysis. Transmittance of a lossy fibre junction consisting of the single-mode and bimodal segments is evaluated. Error in the scalar approximation is proved to increase significantly near the cutoff frequency. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 7]
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