Spot size expansion for improved OEIC-to-fibre coupling using directional couplers with 2D confinement

In optical fibre applications, by using an intermediate multiguide directional coupler section, this work has shown that the field profile of the source laser used can be expanded to match that of the receiving optical fibre. The vector H-field finite element method has been employed to determine the modal propagation constants and vector field profiles. An accurate calculation of the excited modal coefficients was achieved by using the least squares boundary residual method, which satisfies the continuity of the transverse field components more rigorously than through the use of the simple overlap integral approach