Leaky modes in active three-layer slab waveguides

We present a comprehensive numerical mode calculation based on a phenomenological theory for a three-layer slab waveguide with a refractive-index depression but finite gain in the centre region (leaky modes). The leaking rays and the refraction loss of the modes are discussed as well as their influence on the threshold conditions for typical stripe-geometry laser structures. Special attention is paid to the transition regime between refractive-index depression and enhancement. i.e. between leaky-mode `antiguiding¿ and mode `guiding¿. The results are compared with simple analytical formulas available from the literature.