Fibre mode expansion for 2-D waveguide calculations

A numerical method is introduced which is devised to calculate the lower-order modes of optical waveguides with two-dimensional transverse index profiles embedded in a homogeneous cladding medium. We propose a method based on a series expansion using guided modes of an optical fibre. To test the method, it is applied to a three-layer optical-fibre and the results are compared with the exact analytical solutions. The error in the calculation of the modal effective indices is found to be less than 10−6. This method allows the modelling of symmetric 2 × 2 completely fused fibre couplers. Effective indices and polarization corrections are compared with results obtained by the field correction method. The adiabaticity criterion is calculated for these couplers. This revised version was published online in November 2006 with corrections to the Cover Date.