Mode-expander optimisation for high-speed lasers

Summary form only. Mode-expanded lasers are an attractive solution for the high-data-rate low-cost sources required in data communications applications. Improved matching between the active region of the laser and the core of the optical fibre allows both increased power coupling into fibre and a relaxed alignment tolerance for low-cost automated fibre alignment. Tapered waveguides which narrow towards the output facet are widely used to force the optical mode into a more weakly guiding region, leading to an optical mode with a cross-sectional area more closely matched to that of the fibre. Efficient tapers are however long, leading to compromised high speed laser performance, and shortening the taper may lead to scattering from abrupt waveguide truncations and spectral anomalies. In this work, an active beam propagation model is used to optimise waveguide designs under lasing conditions.